rlyb-20231231

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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

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FORM 10-K

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(Mark One)

For the fiscal year ended December 31, 2023

Commission File Number 001-40693

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RALLYBIO CORPORATION

(Exact name of Registrant as specified in its Charter)

____________________________________

(Address of principal executive offices) (Zip Code)

Registrant’s telephone number, including area code: (203) 859-3820

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Securities registered pursuant to Section 12(b) of the Act:

Title of each class TradingSymbol(s) Name of each exchange on which registered

Common Stock, par value $0.0001 per share RLYB The NASDAQ Global Select Market

Securities registered pursuant to Section 12(g) of the Act: None

Indicate by check mark if the Registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yes oNox

Indicate by check mark if the Registrant is not required to file reports pursuant to Section 13 or 15(d) of the Act. Yes oNox

Indicate by check mark whether the Registrant: (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the Registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yesx No o

Indicate by check mark whether the Registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the Registrant was required to submit such files). Yesx No o

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

Large accelerated filer o Accelerated filer o

Non-accelerated filer x Smaller reporting company x

Emerging growth company x

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. o

Indicate by check mark whether the registrant has filed a report on and attestation to its management’s assessment of the effectiveness of its internal control over financial reporting under Section 404(b) of the Sarbanes-Oxley Act (15 U.S.C. 7262(b)) by the registered public accounting firm that prepared or issued its audit report. o

If securities are registered pursuant to Section 12(b) of the Act, indicate by checkmark whether the financial statements of the registrant included in the filing reflect the correction of an error to previously issued financial statements. o

Indicate by check mark whether any of those error corrections are restatements that required a recovery analysis of incentive-based compensation received by any of the registrant's executive officers during the relevant recovery period pursuant to §240.10D-1(b) o

Indicate by check mark whether the Registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). YES o NO x

The aggregate market value of the registrant's voting common stock held by non-affiliates as of June 30, 2023 was approximately $134.4 million, based on the closing price of the registrant’s common stock as reported by Nasdaq on that date.

The number of shares of Registrant’s Common Stock outstanding as of March 7, 2024 was 37,811,970.

DOCUMENTS INCORPORATED BY REFERENCE

Portions of the registrant’s Definitive Proxy Statement for its 2024 Annual Meeting of Stockholders scheduled to be held on May 15, 2024, which Definitive Proxy will be filed with the Securities and Exchange Commission not later than 120 days after the registrant’s fiscal year end of December 31, 2023 are incorporated by reference into Part II and Part III of this Annual Report on Form 10-K.

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Cautionary Note Regarding Forward-Looking Statements

This Annual Report on Form 10-K contains forward-looking statements that are based on management’s beliefs and assumptions and on information currently available to management. All statements other than statements of historical facts contained in this Annual Report on Form 10-K are forward-looking statements. In some cases, you can identify forward-looking statements by terms such as “may,” “will,” “should,” “expect,” “plan,” “anticipate,” “could,” “intend,” “target,” “project,” “contemplate,” “believe,” “estimate,” “predict,” “potential” or “continue” or the negative of these terms or other similar expressions, although not all forward-looking statements contain these words. Forward-looking statements include, but are not limited to, statements concerning:

•the initiation, timing, progress, results, and cost of our research and development programs, and our current and future preclinical and clinical studies, including statements regarding the timing of initiation and completion of our clinical trials for RLYB212, RLYB116 and RLYB331, our toxicology program for RLYB212, and the natural history study for our fetal and neonatal alloimmune thrombocytopenia prevention program, and related preparatory work, and the period during which the results of the trials will become available;

•the success, cost and timing of our clinical development of our product candidates, including RLYB212, RLYB116 and RLYB331;

•the potential of our product candidates to treat certain target diseases;

•our ability to initiate, recruit and enroll patients in and conduct our clinical trials at the pace that we project;

•our ability to obtain and maintain regulatory designations allowing for priority review of our product candidates, and our ability to obtain and maintain regulatory approval of our product candidates, and any related restrictions, limitations or warnings in the label of any of our product candidates, if approved;

•our ability to compete with companies currently marketing or engaged in the development of treatments for diseases that our product candidates are designed to target, including paroxysmal nocturnal hemoglobinuria and generalized myasthenia gravis;

•our reliance on third parties to conduct our clinical trials;

•enhancements to the manufacturing process for RLYB116, and the expected timing of completion thereof;

•our reliance on third parties to manufacture drug substance and drug product for use in our clinical trials;

•the size and growth potential of the markets for RLYB212, RLYB116, RLYB114, RLYB331 and any of our current product candidates or other product candidates we may identify and pursue, and our ability to serve those markets;

•our ability to enter into collaborations, partnerships and other transactions with third parties;

•our ability to identify and advance through clinical development any additional product candidates;

•the commercialization of our current product candidates and any other product candidates we may identify and pursue, if approved, including our ability to successfully build commercial infrastructure or enter into collaborations with third parties to market our current product candidates and any other product candidates we may identify and pursue;

•our ability to retain and recruit key personnel;

•our ability to obtain and maintain adequate intellectual property rights;

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•our expectations regarding government and third-party payor coverage and reimbursement;

•our estimates of our expenses, ongoing losses, capital requirements and our needs for or ability to obtain additional financing;

•our expected uses of the net proceeds from our initial public offering and any subsequent offerings;

•the potential benefits of strategic collaboration agreements and arrangements, including our agreements with Exscientia Limited and AbCellera Biologics Inc. and our research collaboration with EyePoint Pharmaceuticals, Inc., and the expected timing of updates related thereto, our ability to enter into strategic collaborations or arrangements, including potential business development opportunities and potential licensing partnerships, and our ability to attract collaborators with development, regulatory and commercialization expertise;

•our expectations regarding the time during which we will be an emerging growth company under the Jumpstart Our Business Startups Act of 2012;

•our financial performance;

•developments and projections relating to our competitors or our industry; and

•other risks and uncertainties, including those listed under the section titled “Risk Factors.”

The forward-looking statements in this Annual Report on Form 10-K are only predictions and are based largely on our current expectations and projections about future events and financial trends that we believe may affect our business, financial condition and results of operations. These forward-looking statements speak only as of the date of this Annual Report on Form 10-K and are subject to a number of known and unknown risks, uncertainties and assumptions, including those described under the sections in this Annual Report on Form 10-K entitled “Risk Factors” and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” and elsewhere in this Annual Report on Form 10-K. Because forward-looking statements are inherently subject to risks and uncertainties, some of which cannot be predicted or quantified and some of which are beyond our control, you should not rely on these forward-looking statements as guarantees of future events. The events and circumstances reflected in our forward-looking statements may not be achieved or occur and actual future results, levels of activity, performance and events and circumstances could differ materially from those projected in the forward-looking statements. Moreover, we operate in an evolving environment. New risks and uncertainties may emerge from time to time, and it is not possible for management to predict all risks and uncertainties. Except as required by applicable law, we are not obligated to publicly update or revise any forward-looking statements contained herein, whether as a result of any new information, future events, changed circumstances or otherwise.

Trademarks

We use Rallybio as a trademark in the United States ("U.S.") and/or in other countries. This Annual Report on Form 10-K contains references to our trademark and to those belonging to other entities, including Affibody®. Solely for convenience, trademarks and trade names referred to in this Annual Report on Form 10-K, including logos, artwork and other visual displays, may appear without the ® or TM symbols, but such references are not intended to indicate in any way that we will not assert, to the fullest extent under applicable law, our rights or the rights of the applicable licensor to these trademarks and trade names. We do not intend our use or display of other entities’ trade names, trademarks or service marks to imply a relationship with, or endorsement or sponsorship of us by, any other entity.

Risk Factor Summary

Our business is subject to a number of risks that are discussed more fully in the “Risk Factors” section of this Annual Report on Form 10-K. These risks include the following:

•We have incurred significant losses since our inception and anticipate that we will continue to incur losses in the foreseeable future. We have not commercialized any products and have never generated

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revenue from the commercialization of any product. We are not currently profitable, and we may never achieve or sustain profitability;

•We will require significant additional capital to fund our operations, and if we fail to obtain necessary financing, we may not be able to complete the development and commercialization of RLYB212, RLYB116 or any additional product candidates we may develop;

•Raising additional capital may cause dilution to our stockholders, restrict our operations or require us to relinquish rights to our technologies or product candidates;

•We are heavily dependent on the success of RLYB212 and RLYB116, which are in early-stage clinical development. If we are not able to develop, obtain regulatory approval for, or successfully commercialize our product candidates, or if we experience significant delays in doing so, our business will be materially harmed;

•We may not be successful in our efforts to identify additional product candidates. Due to our limited resources and access to capital, we must prioritize development of certain product candidates, the choice of which may prove to be wrong and adversely affect our business;

•Preclinical studies and clinical trials are expensive, time consuming and difficult to design and implement, and involve uncertain outcomes. Any product candidates that we advance into clinical trials may not achieve favorable results in later clinical trials, if any, or receive marketing approval. We may incur additional costs or experience delays in completing, or ultimately be unable to complete, the development and commercialization of our product candidates;

•Enrollment and retention of patients in clinical trials is an expensive and time-consuming process and could be made more difficult or rendered impossible by multiple factors outside our control, including our focus on rare diseases;

•Results of preclinical studies, clinical trials or analyses that we may announce or publish from time to time, may not be indicative of results obtained in later trials, and any interim results we may publish could be different than final results;

•Any product candidates that we develop or the administration thereof, may cause serious adverse events or undesirable side effects, which may halt their clinical development, delay or prevent marketing approval, or, if approved, require them to be taken off the market, include safety warnings, or otherwise limit their sales;

•The regulatory approval processes of the U.S. Food and Drug Administration (the "FDA"), the European Medicines Agency (the "EMA"), and comparable foreign regulatory authorities, including the Medicines and Healthcare products Regulatory Agency in the United Kingdom (the “MHRA”), are lengthy, time-consuming, and inherently unpredictable, and if we are ultimately unable to obtain regulatory approval for RLYB212, RLYB116 or any of our other product candidates, our business will be substantially harmed;

•Our product candidates target rare diseases and conditions, and the market opportunities for RLYB212, RLYB116 or any of our other product candidates, if approved, may be smaller than we anticipate. As a result, our commercial opportunity may be limited and because the target populations of our product candidates are for rare diseases, we must be able to successfully identify patients and capture a significant market share to achieve profitability and growth;

iii

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•The FDA, EMA or other comparable foreign regulatory authorities, including the MHRA, could require the clearance or approval of an in vitro diagnostic or companion diagnostic device as a condition of approval for any product candidate that requires or would commercially benefit from such tests, including RLYB212. Failure to successfully validate, develop and obtain regulatory clearance or approval for companion diagnostics on a timely basis or at all could harm our drug development strategy and we may not realize the commercial potential of any such product candidate;

•We face significant competition from biotechnology and pharmaceutical companies, and our operating results will suffer if we fail to compete effectively;

•We intend to continue to pursue business development transactions focused on the in-license of additional product candidates or the out-license of rights to product candidates in our pipeline and collaborate with third parties for the development and commercialization of our product candidates. We may not succeed in identifying and acquiring businesses or assets, in-licensing intellectual property rights or establishing and maintaining collaborations, which may significantly limit our ability to successfully develop and commercialize our other product candidates, if at all, and these transactions could disrupt our business, cause dilution to our stockholders or reduce our financial resources; and

•If we are unable to obtain, maintain and enforce patent protection for our technology and product candidates, or if the scope of the patent protection obtained is not sufficiently broad, our competitors could develop and commercialize technology and products similar or identical to ours, and our ability to successfully develop and commercialize our technology and product candidates may be adversely affected.

The foregoing is only a summary of some of our risks. For a more detailed discussion of these and other risks you should consider before making an investment in our common stock, see “Risk Factors.”

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Page

PART I.

Item 1. Business 1

Item 1A. Risk Factors 43

Item 1B. Unresolved Staff Comments 98

Item 1C. Cybersecurity 98

Item 2. Properties 99

Item 3. Legal Proceedings 99

Item 4. Mine Safety Disclosure 99

PART II.

Item 7A. Quantitative and Qualitative Disclosures About Market Risk 112

Item 8. Financial Statements and Supplementary Data 112

Item 9A. Controls and Procedures 112

Item 9B. Other Information 113

Item 9C. Disclosure Regarding Foreign Jurisdictions that Prevent Inspections 113

PART III.

Item 10. Directors, Executive Officers and Corporate Governance 113

Item 11. Executive Compensation 113

Item 14. Principal Accounting Fees and Services 113

PART IV

Item 15. Exhibits, Financial Statement Schedules 113

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PART I

Item 1. Business.

Overview

We are a clinical-stage biotechnology company comprised of experienced biopharma industry leaders with extensive research, development, and rare disease expertise with a mission to develop and commercialize life-transforming therapies for patients with severe and rare diseases. Since our launch in January 2018, we have built a broad pipeline of promising product candidates aimed at addressing diseases with unmet medical need in the areas of maternal fetal health, complement dysregulation, hematology, and metabolic disorders. Our two most advanced programs are in clinical development: RLYB212, an anti-HPA-1a antibody for the prevention of fetal and neonatal alloimmune thrombocytopenia (“FNAIT”) and RLYB116, an inhibitor of complement component 5 (“C5”), with the potential to treat several diseases of complement dysregulation. Both programs have completed Phase 1 clinical trials, and we currently plan to initiate a Phase 2 clinical trial of RLYB212 in the second half of 2024.

Our Approach

At Rallybio Corporation (“Rallybio” or the "Company"), we do not accept that millions of patients suffering from devastating rare diseases should have to live without transformative treatments. There are an estimated 25 to 30 million people affected by as many as 7,000 rare diseases in the United States alone, with a significantly greater number affected globally. Our goal is to transform the lives of these individuals through the development of therapeutics that provide meaningful clinical benefits.

We believe the long-term success of the Company is built on our key strengths:

•Our team’s proven execution capability to drive product candidates through clinical development to marketing approvals. We have assembled a team with a proven history of successfully advancing product candidates from discovery toclinical development and through marketing approval. Members of our team have played critical roles in the approval of more than 30 drugs, including seven approvals for rare disease therapeutics since 2013, and secured approvals from regulatory authorities in the Americas, Europe, Australia, and Asia. In doing so, our employees previously developed and implemented novel clinical trial designs and successfully conducted clinical trials in previously underserved patient populations, including those impacted by diseases lacking approved therapies. We believe this collective prior experience positions us to efficiently and expertly execute at each step in the research and development process and enhances the value we can bring to our product candidates and patients.

•Our extensive knowledge of rare diseases and our scientific expertise positions us to identify therapies with the potential for transformative impact. Althoughwe intend to focus our near-term efforts on maximizing the value of our current portfolio, we may in the future opportunistically seek to acquire and develop product candidates that possess a clear mechanism ofaction and that aim to address diseases with a well-understood pathophysiology for which there is a significant unmet medical need. We believe that a product candidate’s mechanism of action should target the causal biology of the disease to provide the highest probability of dramatically improving the lives of patients. We also believe that our team’s extensive experience in rare diseases and overall deep scientific expertise position us to identify opportunities where these links can be made. In addition, our ability to source these product candidates is facilitated by our extensive network of relationships with leaders in industry and in academic centers worldwide.

Our Team

Our Chief Executive Officer, Stephen Uden, M.D., and Executive Chairman, Martin W. Mackay, Ph.D., previously worked together in different organizations to successfully build, develop, and launch transformative therapies for patients with rare diseases. In addition, several members of our team were integral in the successful development and/or approval of therapies such as Strensiq (asfotase alfa) for patients with perinatal-, infantile-, and juvenile-onset hypophosphatasia ("HPP"), Kanuma (sebelipase alfa) for patients with lysosomal acid lipase deficiency, Nulibry (fosdenopterin) for patients with molybdenum cofactor deficiency, Soliris (eculizumab) for patients with refractory generalized myasthenia gravis ("gMG"), Soliris for patients with relapsing neuromyelitis optica spectrum disorder ("NMOSD"), Ultomiris (ravulizumab-cwvz) for patients with paroxysmal nocturnal hemoglobinuria ("PNH") and Ultomiris for patients with atypical hemolytic uremic syndrome ("aHUS").

Our Pipeline

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Our pipeline is illustrated in the chart below:

FNAIT: Fetal and neonatal alloimmune thrombocytopenia; HPA-1a: Human platelet antigen-1a; C5: Complement component 5; ABD: Albumin-binding domain; HPP: Hypophosphatasia; ENPP1: Ectonucleotide pyrophosphatase/phosphodiesterase 1

*Disease areas under consideration: hematology, including disorders such as PNH and antiphospholipid syndrome; and neurology, including disorders such as gMG

** Rallybio and EyePoint Pharmaceuticals are conducting an evaluation to assess the viability of using EyePoint's delivery technology with Rallybio's complement inhibitor; following the evaluation, the parties will determine whether to advance the collaboration, in which case EyePoint would assume development rights

Prevention of FNAIT

We are developing RLYB212 for the prevention of FNAIT. FNAIT is a potentially life-threatening rare disease that can cause uncontrolled bleeding in fetuses and newborns that can arise during pregnancy due to an immune incompatibility between an expectant mother and her fetus in a specific platelet antigen called human platelet antigen 1 ("HPA-1"). This incompatibility can cause an expectant mother to develop antibodies that attack the platelets of her fetus. The destruction of platelets in the fetus can result in severely low platelet counts, or thrombocytopenia, potentially leading to devastating consequences including miscarriage, stillbirth, death of the newborn, or severe lifelong neurological disability in those babies who survive. There is currently no approved therapy for the prevention or treatment of FNAIT.

We estimate that there are over 22,000 pregnancies at high risk of developing FNAIT each year in the United States, Canada, the United Kingdom (the "UK"), other major European countries and Australia. Since, there are no approved therapies to prevent FNAIT, expectant mothers are not currently screened for the risk of FNAIT. As a result, the vast majority of pregnancies at risk for FNAIT go unidentified and untreated. In those pregnancies that are identified as at-risk, typically due to the delivery of a prior FNAIT affected child, expectant mothers may be treated with weekly intravenously-administered high doses of immunoglobulin G ("IVIG"), along with the oral steroid immunosuppressant prednisone. However, IVIG administration does not prevent the immune response, called alloimmunization, and is costly, time-intensive, difficult to tolerate and associated with significant treatment-related complications. Based on the data generated to date and the clinical precedent for effective prevention of maternal alloimmunization by anti-RhD prophylaxis, which has resulted in the virtual elimination of Rhesus disease, we believe that targeting HPA-1a with an anti-HPA-1a antibody has the potential to drive rapid elimination of HPA-1a positive platelets from the circulation of expectant mothers, prevent alloimmunization and thereby prevent the occurrence of FNAIT.

We have completed two RLYB212 clinical trials: a Phase 1 first-in-human clinical trial and a Phase 1b proof of concept clinical trial. The Phase 1 first-in-human clinical trial was a single-blind, placebo-controlled study that investigated the safety and pharmacokinetics (“PK”) of subcutaneous (“SC”) administration of RLYB212 in HPA-1a negative healthy participants. The clinical trial included a single dose cohort and a multiple dose cohort. In the multiple dose cohort, subjects received SC RLYB212 or placebo every two weeks for 12 weeks. We reported preliminary results from the multi-dose cohort in the fourth quarter of 2023. The data and our clinical pharmacology modeling predictions support a once monthly dosing regimen for the planned Phase 2 clinical trial. RLYB212 was observed to be generally well-tolerated with no reports of injection site reactions or serious adverse events.

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The Phase 1b single-blind, placebo-controlled proof-of-concept clinical trial was designed to establish the ability of SC RLYB212 to rapidly eliminate HPA-1a positive platelets transfused to HPA-1a negative healthy subjects. The study included 11 males aged 18 to 65 years, randomized to RLYB212 0.09mg (n=4), RLYB212 0.29mg (n=5), or placebo (n=2). We reported the results from this trial at the 31st Congress of the International Society on Thrombosis and Haemostasis ("ISTH") in the second quarter of 2023. The results showed that SC RLYB212 administration produced a dose-dependent, rapid, and complete elimination of transfused HPA-1a positive platelets in HPA-1a negative subjects, with both doses meeting the prespecified proof-of-concept criteria of ≥90% reduction in mean platelet elimination half-life. Mean platelet elimination half-life was 5.8 hours (0.09mg dose) and 1.5 hours (0.29mg dose) for RLYB212 compared to 71.7 hours for placebo. Consistent with the Phase 1 first-in-human trial, RLYB212 was observed to be well-tolerated with no reports of serious or severe adverse events.

Additionally, we are conducting a FNAIT Natural History Alloimmunization Study ("FNAIT natural history study"). This prospective, non-interventional, multinational natural history study is designed to screen up to 30,000 expectant mothers presenting at gestational week 10 to 14 prenatal visit to determine the frequency of women at higher FNAIT risk among expectant mothers of different racial and ethnic characteristics, as well as the frequency of HPA-1a alloimmunization and pregnancy outcomes among these women. Subject to future discussions with regulatory authorities, we expect that data from this study will contribute to a control dataset for a future single-arm Phase 3 registrational clinical trial for RLYB212. An additional objective of the FNAIT natural history study is to operationalize de novo the laboratory screening test paradigm for FNAIT risk and generate FNAIT laboratory test performance data that we plan to use for future regulatory discussions. As of March 1, 2024, approximately 9,400 women have been screened as part of the study.

Treatment of Disorders Due to Complement Dysregulation

The complement system plays a central role in innate immunity, as well as, shaping adaptive immune response. Dysregulation of the complement pathway has been implicated in the pathogenesis of a growing number of diseases, making it an attractive target for therapeutic intervention. Antibody inhibitors of C5 have been successfully developed to treat diseases caused by complement pathway dysregulation, including PNH, aHUS, refractory gMG and relapsing NMOSD. Despite the approval of antibody-based C5 inhibitors for patients with these diseases, we believe there remains a significant need in the market for safe, effective, patient-friendly, and accessible therapies.

Our team has a track record of success in designing, developing, and securing marketing approval for C5 complement inhibitors, including Soliris and Ultomiris, for patients around the world with severe and rare complement-mediated diseases. Our most advanced product candidate in this therapeutic area is RLYB116, an inhibitor of C5, which is a central component of the terminal complement pathway. RLYB116 is an Affibody molecule attached to an albumin binding domain that has the potential to drive the rapid, complete, and sustained inhibition of C5 with a SC injection. We have completed a Phase 1 clinical trial in healthy participants that included the study of RLYB116 as both a single ascending dose (“SAD”) and a multiple ascending dose (“MAD”).

The SAD portion of the RLYB116 Phase 1 trial included five cohorts with doses ranging from 2mg up to 300mg. Data from the SAD portion of the RLYB116 trial showed that all study participants that were administered a single 1 mL SC injection of 100 mg of RLYB116 (n=6) demonstrated a reduction in free C5 greater than 99% within 24 hours of dosing. Subcutaneously administered RLYB116 in the SAD portion of the trial was observed to be generally well-tolerated at the 100 mg dose, with mild adverse events and no drug-related serious adverse events reported. The terminal elimination half-life of RLYB116 was greater than 300 hours. The MAD portion of the RLYB116 Phase 1 trial included an adaptive single-blind design with a four-week treatment duration to evaluate the safety, tolerability, PK, and pharmacodynamics ("PD") of RLYB116 with multiple dose SC administration. The MAD portion of the trial included four cohorts: Cohort 1 (weekly dosing of 100 mg), Cohort 2 (3 doses of 100 mg the first week followed by weekly dosing), Cohort 3 (150 mg weekly dosing reduced to 125 mg weekly dosing) and Cohort 4 (75 mg twice the first week followed by 100 mg twice per week) with post-treatment for 10 weeks. In December 2023, we reported data from the MAD portion of the trial that demonstrated a 100 mg low volume (1 mL) once-weekly dose of subcutaneously administered RLYB116 achieved sustained mean reductions in free C5 of greater than 93%, including at Day 29 with measurement prior to the last dose. The reduction from pre-treatment free C5 at 24 hours after the first dose of 100 mg was greater than 99%. In the MAD portion of the Phase 1 trial, RLYB116 demonstrated low inter-subject variability and consistent increases in exposure relative to dose with a mean estimated elimination half-life for RLYB116 of

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>300 hours. RLYB116 administered in the MAD trial as a 100 mg once-weekly dose was also observed to be generally well tolerated.

Based on data from the MAD portion of the Phase 1 trial and additional work we have conducted with RLYB116, we believe that RLYB116 has the potential to be an effective treatment for patients with certain complement-mediated diseases, including gMG. We have prioritized enhancements to the manufacturing process that are intended to improve tolerability at higher doses with a low injection volume and infrequent SC administration, thereby opening up the opportunity to treat a wider range of complement-mediated diseases in addition to gMG, including PNH and antiphospholipid syndrome. We expect the manufacturing work to be completed in the second half of 2024.

Our second C5 inhibitor, RLYB114, is a pegylated C5-targeted Affibody molecule with PK properties designed for the treatment of complement-mediated ophthalmic diseases. In February 2023 we entered into a collaboration with EyePoint Pharmaceuticals, Inc. (“EyePoint”) and are using EyePoint’s proprietary technology for sustained intraocular drug delivery, with the initial focus on geographic atrophy, an advanced form of age-related macular degeneration that leads to irreversible vision loss. Rallybio and EyePoint expect to provide an update on this collaboration in the first half of 2024.

Hematological Disorders

In May 2022, we obtained worldwide exclusive rights to RLYB331, a preclinical, monoclonal antibody that is designed to inhibit Matriptase-2 ("MTP-2"). The inhibition of MTP-2 significantly increases levels of hepcidin, decreases iron load and treats ineffective erythropoiesis. We believe RLYB331 has the potential to address a significant unmet need for patients with severe anemia with ineffective red blood cell production or erythropoiesis and iron overload, such as polycythemia vera, beta thalassemia and a subset of myelodysplastic syndromes ("MDS"), amongst others. Currently these patients are underserved by the existing standard of care. We are continuing with preclinical activities to support the transition of RLYB331 into clinical development and expect to report data from this program in the first half of 2024.

Artificial Intelligence Drug Discovery Collaboration

In July 2019, we formed a joint venture with Exscientia Limited ("Exscientia"), an Oxford, UK-based artificial intelligence ("AI") and machine learning drug discovery company with a proprietary chemical design platform to discover novel small molecule drug candidates. Our joint venture is focused on the discovery and development of small molecule therapeutics for the treatment of patients with rare metabolic diseases.

The joint venture is currently developing a small molecule targeting an Ectonucleotide Pyrophosphatase/ Phosphodiesterase 1 ("ENPP1") inhibitor for the treatment of HPP. HPP is a rare, genetic disease characterized by mutations in the ALPL gene. The ALPL gene provides instructions for making an enzyme called tissue-nonspecific alkaline phosphatase, which plays an important role in the growth and development of bones and teeth. The incidence of HPP has been reported to be 1 in 100,000 to 1 in 300,000 (United States and Canada) for severe disease and 1 in 6,370 (European Union) for less severe forms. These mutations lead to diminished activity of the alkaline phosphatase enzyme and the accumulation of inorganic pyrophosphate (“PPi”), which inhibits bone mineralization causing multiple skeletal pathologies. We believe that a small molecule inhibitor of ENPP1 has the potential to bring meaningful benefit to HPP patients by reducing excess levels of pyrophosphate, thereby removing an inhibitor of calcium mineralization and bone formation.

We and Exscientia continue to work toward the selection of a small molecule development candidate to advance into the clinic targeting ENPP1 for the treatment of patients with HPP. Proof of mechanism studies are in progress with a leading global HPP expert. We plan to provide an update on the progress of the program in the second half of 2024.

AbCellera Collaboration

In December 2022, we entered into a strategic alliance to discover, develop, and commercialize novel antibody-based therapeutics for rare diseases. This multi-year, multi-target collaboration will combine AbCellera Biologic's ("AbCellera") antibody discovery engine with Rallybio’s clinical and commercial expertise in rare diseases to identify optimal clinical candidates with a goal of delivering therapies to patients.

AbCellera and Rallybio will co-develop up to five rare disease therapeutic targets, which will be chosen together by both companies. The collaboration will allow Rallybio to add product candidates to our existing pipeline with the option for AbCellera to conduct process development and clinical manufacturing activities. The first program is focused on addressing the significant unmet therapeutic needs of patients with rare metabolic diseases.

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Our Strategy

Our mission is aligned with our expertise: to identify and accelerate the development of life-transforming therapies for patients with severe and rare disorders. To achieve this mission, our strategy includes the following key components:

•Establish a leading rare disease company with a team that delivers transformative medicines to patients. We believe our team’s expertise and knowledge are fundamental to our long-term success. Our research and development team is led by experienced drug development executives who were integral in the approvals of more than 30 drugs from leading companies, including Alexion Pharmaceuticals, Inc, Astellas Pharma Inc., Pfizer Inc. and Wyeth, LLC. We plan to create value by continuing to leverage our team’s expertise and focus on further development of our current product candidates either alone or through partnerships and collaborations to significantly improve the lives of patients.

•Advance RLYB212 for the prevention of FNAIT. There is currently no approved therapy for the prevention of FNAIT. Women at higher risk of FNAIT may experience potentially devastating outcomes and we believe there is a significant unmet need for patients. We believe the clinical data generated to date support continued investment and development of RLYB212 and provide us with an opportunity to deliver a substantially impactful therapeutic in maternal fetal health for expectant mothers with FNAIT. Furthermore, we estimate that the market opportunity exceeds $1 billion. We plan to initiate a Phase 2 study in expectant mothers at higher risk of FNAIT in the second half of 2024.

•Advance RLYB116 for the treatment of diseases of complement dysregulation through partnering or other forms of non-dilutive financing. In the fourth quarter of 2023, we announced preliminary data from a MAD Phase 1 trial of RLYB116. Based on the data from this trial, we believe that RLYB116 has the potential to be an effective treatment for patients with certain complement-mediated diseases, including gMG. We are currently implementing additional manufacturing process improvements that we believe will enable RLYB116 to treat a broader range of complement-mediated diseases. Given our desire to conserve capital, we will seek to move this program forward with a partner or non-dilutive financing.

•Leverage the progress made to date and maximize the value from our preclinical candidates, including the programs in our collaborations with Exscientia and AbCellera. We believe that our preclinical pipeline programs have significant potential to generate value by meeting the unmet needs of patients and we intend to continue to move these forward in a capital-efficient manner. For example, we are currently conducting preclinical work for RLYB331 and expect to report the results of this work in the first half of 2024 prior to initiating any further development work. In addition, we are continuing to support our collaborations with Exscientia and AbCellera with a goal of generating additional data from these programs that can inform the most appropriate next steps in development.

•Create value from our pipeline through targeted business development activities. We believe we have assembled a valuable portfolio of product candidates targeting several rare diseases and will seek to unlock that value by leveraging our current and potential future partnerships and collaborations for one or more of these programs. We believe this will enable us to advance these programs while focusing our development efforts and related spend on RLYB212. We may also periodically evaluate the potential in-license or acquisition of new programs subject to market conditions and our cash runway.

Our Product Candidates

RLYB212 for the prevention of FNAIT

RLYB212 is a subcutaneously administered monoclonal anti-HPA-1a antibody for the prevention of FNAIT, a maternal fetal blood disorder that can cause potentially devastating outcomes in the fetus or neonate including miscarriage, neonatal death, and severe life-long neurological disability in the babies that survive. We have completed two Phase 1 clinical trials for RLYB212 and we intend to initiate the Phase 2 clinical trial for RLYB212 in the second half of 2024. Based on the preclinical and clinical data to date and our understanding of FNAIT, we believe RLYB212 has the potential to prevent maternal alloimmunization and thereby the occurrence of FNAIT.

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We are also currently conducting an FNAIT natural history study. This prospective, non-interventional, multinational study is designed to determine the frequency of women at higher FNAIT risk among expectant mothers of different racial and ethnic characteristics, as well as the frequency of HPA-1a alloimmunization and pregnancy outcomes among these women. We expect that data from this study will contribute historical control data to support a planned single-arm Phase 3 registrational clinical trial of RLYB212. An additional objective of the FNAIT natural history study is to operationalize de novo the laboratory screening test paradigm for FNAIT risk and generate FNAIT laboratory test performance data for future regulatory discussions.

Maternal fetal blood disorders

FNAIT is one of several devastating disorders that is caused by an immune incompatibility of a mother and fetus during pregnancy. One of the best-characterized prenatal immune incompatibility disorders is Rh disease. This condition arises when the mother is RhD negative and her fetus is RhD positive. RhD incompatibility may lead to destruction of red blood cells in the fetus and can result in severe outcomes including miscarriage or loss of a newborn. Rh disease is treated by giving at-risk expectant mothers low doses of antibodies to RhD. These antibodies remove fetal red blood cells that have crossed into the mother’s circulation, thereby preventing her from developing an immune response that could destroy the red blood cells in the fetus. Since the approval of the first Rho (D) Immune Globulin in 1968, known as RhoGAM, expectant mothers in many countries, including in North America and Europe, are routinely screened for their RhD status, and Rh disease is largely prevented in at-risk expectant mothers. We are pursuing a similar approach to prevent FNAIT.

FNAIT disease background

Like Rh disease, FNAIT is a disorder that occurs during pregnancy when an expectant mother’s immune system attacks a specific antigen on the blood cells of her fetus, leading to their destruction. This results in an increased risk of bleeding in the fetus and newborn. In the majority of cases, the effects of FNAIT are mild; however, up to 20% of FNAIT cases experience intracranial hemorrhage ("ICH"), which can lead to devastating outcomes such as miscarriage, stillbirth, loss of the newborn and severe lifelong neurological disabilities in those babies that survive.

FNAIT is caused by a mismatch in the type of HPA-1 that is expressed by the expectant mother and the fetus. There are two predominant forms of HPA-1, known as HPA-1a and HPA-1b, which are expressed on the surface of platelets. These two alleles differ by a single amino acid. Individuals who are homozygous for HPA-1b, meaning that they have two copies of the HPA-1b allele and no copies of the HPA-1a allele, are also known as HPA-1a negative. Upon exposure to HPA-1a, these individuals can develop antibodies to that antigen in a process known as alloimmunization. In expectant mothers, alloimmunization can occur upon mixing of fetal blood with maternal blood. When alloimmunization occurs in an expectant mother, the anti-HPA-1a antibodies that develop in the mother can cross the placenta and destroy platelets in the fetus.

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Pathophysiology of FNAIT

There are no approved therapies to treat or prevent FNAIT and expectant mothers are not currently screened for FNAIT risk. Today, expectant mothers at risk of FNAIT are typically only identified following the delivery of an FNAIT affected child. These mothers may be treated during subsequent pregnancies with weekly administration of IVIG, along with the oral steroid immunosuppressant prednisone. While IVIG administration can potentially mitigate the detrimental effects of anti-HPA-1a antibodies, it does not prevent alloimmunization, is costly, time-intensive, difficult to tolerate and associated with significant treatment-related complications.

Babies with FNAIT are typically diagnosed at the time of delivery by the presence of low platelet counts identified during routine analysis, the presence of petechiae on the skin or due to the manifestations of severe complications such as ICH or gastrointestinal bleeding. Upon diagnosis, babies with FNAIT may receive platelet transfusions and may be admitted to the neonatal intensive care unit. In severe cases, babies may suffer life-long neurological disability or may not survive.

Based on published data, we believe that there are at least 22,000 pregnancies annually that are at high risk of FNAIT in the United States, Canada, the UK, other major European countries, and Australia. These pregnancies represent expectant mothers who are HPA-1a negative, who are at high risk of alloimmunization and who are carrying an HPA-1a positive fetus.

Studies show that approximately 2% of the Caucasian population is HPA-1a negative. Based on this frequency and live birth rates of Caucasian women from 2018, we estimate that there are approximately 110,000 HPA-1a negative expectant mothers in the aforementioned countries each year. From this population of expectant mothers, a subset is at higher risk of FNAIT due to the presence of a specific HLA allele, known as DRB3*01:01. Genetic studies have found that expectant mothers who have this specific HLA allele are approximately 25 times more likely to develop antibodies to HPA-1a than those without this allele. This higher-risk population represents approximately 27% of HPA-1a negative expectant mothers, or approximately 30,000 individuals.

From this higher-risk population, an estimated 89% of women would not already have antibodies to HPA-1a and, of these, an estimated 86% would be expected to be carrying an HPA-1a positive fetus. We believe this portion of the higher-risk population could potentially benefit from administration of a monoclonal anti-HPA-1a antibody such as RLYB212.

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Pregnancies At High Risk of FNAIT Each Year

*Source: NCHS National Vital Statistics Report Volume 68, Number 13, November 30, 2019, Births: Final Data for 2018; World Bank Population Data (2018); Kjeldsen-Kragh, et al Blood 2007; Hardy-Weinberg estimate; Kjeldsen-Kragh et al Blood 110, 833-839 (2007)

Given the well-established prevalence of HPA-1a negativity in the Caucasian population, our current estimates of the FNAIT at-risk population are derived from the estimated proportion of Caucasian births from approximately eight million live births per year in the above-mentioned countries. We are committed, however, to ensuring that all expectant mothers of any race or ethnicity who are at high risk of FNAIT are identified and eligible for treatment. To this end, we are conducting a FNAIT natural history study, in part to obtain more precise prevalence estimates of the FNAIT at-risk population in racial and ethnic groups that may have been underrepresented in previously published studies. We believe that data from this study will more precisely inform the size of the FNAIT at-risk population.

We believe that screening for FNAIT risk can be performed routinely and cost effectively as part of standard prenatal testing provided to expectant mothers during pregnancy. Testing for maternal HPA-1 type and presence of the HLA-DRB3*01:01 allele could occur during the first trimester, and at the same time as other routine blood work and risk screening. We don’t expect that an additional blood draw would be required. Importantly, U.S. and EU physicians have advised that our approach and timing for FNAIT screening would fit well within the established first trimester prenatal testing paradigm and could be performed at the same time as routine blood typing and Rh testing. Based on our global market research with maternal-fetal medicine specialists, obstetricians-gynecologists and payers, we believe there is high awareness of the catastrophic impact of FNAIT, and a strong desire to both screen and provide preventive therapy to at-risk expectant mothers if there were an approved product to prevent FNAIT and affordable screening tests.

We believe screening and preventive treatment can have a significant impact on this potentially devastating disease. For example, screening and treatment in Rh disease have been highly effective in reducing the number of affected births. In developed countries with access to prenatal testing and treatment, the prevalence of Rh disease is 2.5 per 100,000 compared to 276 per 100,000 worldwide. We believe that applying a similar approach to the prevention of FNAIT could lead to a significant reduction in the number of babies at risk for FNAIT. In our FNAIT natural history study, we are using screening tests for maternal HPA-1 type, maternal HLA-DRB3*D1:01 status, maternal HPA-1a antibodies and fetal HPA-1 genotype.

Our solution: RLYB212

RLYB212 preclinical data

A mouse model of FNAIT has been created in which the amino acids comprising the HPA-1a antigen are reconstituted in the mouse gene. These transgenic mice (referred to as APLDQ mice based on the amino acid changes) recapitulate multiple aspects of FNAIT. Administration of anti-HPA-1a antibodies to APLDQ mice leads to destruction of APLDQ platelets and severe thrombocytopenia. Injection of platelets from APLDQ mice into wild-type mice can induce an HPA-1a specific immune response. Finally, wild-type female mice pre-immunized with APLDQ platelets, when bred with APLDQ male mice, give birth to severely thrombocytopenic pups, many of which exhibit an accompanying bleeding phenotype. Treatment of these pregnant female mice with IVIG resulted in lowering the level of anti-APLDQ antibodies in the fetus and a reduction in thrombocytopenia.

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In a prophylactic treatment model, a single large bolus intravenous injection of 1 x 108 APLDQ platelets (equivalent to about one-sixth of the total blood volume in the host) was administered to wild-type mice. At a dose of 0.4 μg (yielding a peak concentration of approximately 0.2 μg/ml), RLYB212 was able to drive rapid and complete elimination of APLDQ platelets, as shown in the first graph below, and prevent a host antibody response, as shown in the second graph below. Also shown in the graphs below, this dose correlates to a concentration of RLYB212 projected to bind approximately 10% of the HPA-1a antigen present on the transfused APLDQ platelets. Thus, the approximately 10% receptor binding is sufficient to clear platelets and prevent alloimmunization in the mouse model.

RLYB212 Clinical Development

We have completed two RLYB212 clinical trials, a Phase 1 first-in-human trial and a Phase 1b proof-of-concept trial. The Phase 1 first-in-human clinical trial is a single-blind, placebo-controlled study that investigated the safety and PK of SC administration of RLYB212 in HPA-1a negative healthy participants. The clinical trial included a single dose cohort and a multiple dose cohort. In the multiple dose cohort, subjects received SC RLYB212 or placebo every two weeks for 12 weeks. An overview of the study's design is illustrated below.

Phase 1 PK and Safety Study of RLYB212 in HPA-1a Negative Healthy Participants

We reported preliminary results from the multi-dose cohort in the fourth quarter of 2023. The data demonstrated that multiple dose PK were consistent both within and between subjects. The data and our clinical pharmacology modeling predictions support a once monthly dosing regimen for the planned Phase 2 study. RLYB212 was observed to be generally well-tolerated with no reports of injection site reactions or serious adverse events.

The Phase 1b single-blind, placebo-controlled proof-of-concept trial was designed to establish the ability of SC RLYB212 to rapidly eliminate HPA-1a positive platelets transfused to HPA-1a negative healthy subjects. The

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study included 11 males aged 18 to 65 years, randomized to RLYB212 0.09mg (n=4), RLYB212 0.29mg (n=5), or placebo (n=2). An overview of the study's design is illustrated below.

Phase 1b Trial of RLYB212 in Healthy Male Participants

In June 2023, we reported the results from this clinical trial at ISTH. The results showed that SC RLYB212 administration produced a dose-dependent, rapid and complete elimination of transfused HPA-1a positive platelets in HPA-1a negative subjects, with both doses meeting the prespecified proof-of-concept criteria of ≥90% reduction in mean platelet elimination half-life. Mean platelet elimination half-life was 5.8 hours (0.09mg dose) and 1.5 hours (0.29mg dose) for RLYB212 compared to 71.7 hours for placebo. Consistent with the Phase 1 first-in-human trial, RLYB212 was observed to be well-tolerated with no reports of serious or severe adverse events.

Both the U.S. FDA and the EMA have designated RLYB212 as an orphan drug. Orphan drug designations offer certain incentives including tax credits, marketing exclusivity upon any approval, fee waivers, and the ability to interact with both agencies to receive specialized regulatory advice and assistance. We recently engaged with the EMA in such a process in advance of our planned Phase 2 clinical trial. We received feedback from the EMA and are now moving forward with our Clinical Trial Application to support conduct of the Phase 2 study in Europe.

Based on the data generated to date and subject to completion of regulatory discussions, we plan to initiate a Phase 2 trial of RLYB212 in expectant mothers at higher FNAIT risk in the second half of 2024. The primary objective of the Phase 2 clinical trial will be to assess the PK and safety of SC RLYB212 administered antenatally in expectant mothers. Additional objectives will include assessing the safety of RLYB212 in the neonate and neonatal exposure of RLYB212 at time of birth, and assessing pregnancy and neonatal outcomes as well as the occurrence of emergent HPA-1a alloimmunization. We are designing the trial as a single-arm, open-label study and plan to conduct the trial in Europe. The intended study population is women who are at higher risk for HPA-1a alloimmunization and FNAIT (i.e., women who are identified through screening to be HPA-1a negative and HLA-DRB3*0101 positive), who are bearing an HPA-1a positive fetus and have not previously alloimmunized. Dosing of RLYB212 will be initiated by gestational week 16 and continued at monthly intervals through pregnancy. An overview of the study's design is illustrated below.

Phase 2 Dose Confirmation Trial of RLYB212 in Expectant Mothers

Prospective FNAIT Natural History Alloimmunization Study

We have an ongoing prospective, non-interventional, multinational natural history study. This study is designed to screen up to 30,000 expectant mothers presenting at gestational week 10 to 14 prenatal visit

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to determine the frequency of women at higher FNAIT risk among expectant mothers of different racial and ethnic characteristics, as well as the frequency of HPA-1a alloimmunization and pregnancy outcomes among these women. Subject to future discussions with regulatory authorities, we expect that data from this study will contribute to a control dataset for a future single-arm Phase 3 registrational clinical trial for RLYB212. An additional objective of the FNAIT natural history study is to operationalize de novo the laboratory screening test paradigm for FNAIT risk and generate FNAIT laboratory test performance data that we plan to use for future regulatory discussions. As of March 1, 2024 approximately 9,400 women have been screened in the study.

RLYB116 for the treatment of disorders due to complement dysregulation

RLYB116 is an inhibitor of complement component C5, a component of the complement pathway which plays a central role in innate immunity as well as shaping adaptive immune response. Dysregulation of the complement pathway has been implicated in the pathogenesis of a growing number of diseases, making it an attractive target for therapeutic intervention. Antibody inhibitors of C5 have been successfully developed to treat diseases caused by immune dysfunction, including PNH, aHUS, refractory gMG and relapsing NMOSD. RLYB116 includes an Affibody molecule, which is an antibody mimetic protein that has a much smaller molecular weight than a traditional antibody and may also be easier and less costly to produce. In contrast to C5-targeted antibody therapeutics that are administered intravenously, RLYB116 has the potential to be administered as a small volume subcutaneous injection. RLYB116 also includes an albumin binding domain, which may extend the half-life of the Affibody domain. In addition, amino acid substitutions that are part of RLYB116 are intended to enhance its stability. We view RLYB116 as a potential pipeline-in-a-product with disease areas under consideration including PNH, gMG and antiphospholipid syndrome. We believe RLYB116 can address significant unmet needs for patients with these diseases by providing a potential treatment that is more accessible and patient-friendly than existing marketed products, including by reducing the frequency and improving the route of administration.

Based on our team’s experience studying and developing therapies targeting the complement system, we believe there are four important attributes that could support clinical and commercial success in the treatment of a broad range of patients suffering from complement-mediated diseases. These include a mechanism of action targeting terminal complement, the ability to produce rapid, complete and sustained inhibition of C5, a safety profile consistent with C5 antibodies currently approved for therapeutic use, and pricing flexibility to treat a broad range of complement-mediated diseases. We believe RLYB116 has the potential to demonstrate these attributes, and if so, could have a life-transforming impact on patients. Given our desire to conserve capital, we may seek a partner or access to non-dilutive financing to support future clinical development.

The complement system

The complement system includes over 30 proteins in plasma and on cell surfaces that support the body’s adaptive or antibody-based immune system in the destruction of pathogenic bacteria. Complement proteins circulate in the blood in an inactive form prior to activation in response to infection. Activation occurs through a pathway of proteolytic cleavage events initiated by pathogen recognition and resulting in pathogen destruction. Three complement pathways that converge on C5 are known and are referred to as the classical, lectin and alternative pathways. In the classical pathway, antibodies bind to antigens, which in turn trigger a protease cascade that activates complement protein C3 and then complement protein C5. Activation of C5 convertase generates C5b which can initiate formation of membrane pores and subsequent lysis of cells. The binding of C5b to host cells is normally prevented by the presence of specific glycoproteins on the cell surface.

gMG disease background

gMG is a potentially life-threatening, rare autoimmune neuromuscular disorder. Patients with gMG develop antibodies that attack critical signaling proteins at the junction between nerve and muscle cells, thereby inhibiting the ability of nerves to communicate properly with muscles. This inhibition leads to muscle weakness, which can occur in ocular muscles leading to droopy eyelids as well as blurred or double vision, and can occur in the muscles in the face, neck, throat and jaw, causing difficulty chewing and swallowing as well as respiratory problems, speech difficulties and weakness in skeletal muscles leading to problems in limb function. While symptoms can be transient and remit spontaneously in the early stages of the disease, as the disease progresses, symptom-free periods become less frequent and disease exacerbations can last for months. Up to 20% of gMG patients experience respiratory crisis at least once in their lives. During such a crisis, a decline in respiratory function can become life-threatening and require intubation and mechanical ventilation. According to a comprehensive epidemiological study of

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gMG in western Denmark from 1975-89, from the time of diagnosis, the overall survival rates at 3, 5, 10, and 20 years are estimated to be 85%, 81%, 69% and 63%, respectively. Patients with gMG suffer from poor quality of life due to the impact of their disease on physical function and the burden of treatment-related adverse events. The prevalence of gMG has been estimated to be at least 100 people per million.

Current treatments for gMG and their limitations

In the first-line setting, patients presenting with symptomatic gMG are commonly treated with acetylcholinesterase inhibitors such as pyridostigmine, to improve neuromuscular transmission. As the disease progresses, patients may receive immunosuppressive therapies off-label; unfortunately, these therapies are associated with a substantial treatment burden and can even lead to a worsening of the disease. Targeted, therapies approved for treatment of gMG include complement inhibitors (e.g., Soliris, Ultomiris, Zilbrysq) and FcRn inhibitors (e.g., Vyvgart, Rystiggo). These treatments have yielded substantial symptom improvements, though unmet need remains for treatments that are more patient-friendly. Rituximab is another treatment used off-label for gMG, though it is believed to have more benefit in patients with anti-muscle-specific tyrosine kinase ("MuSK") antibodies than those with anti-AChR antibodies.

For patients with severe gMG or recurrent exacerbation and crisis, there are a number of methods utilized to reduce circulating IgG antibodies. These procedures include plasma exchange and administration of IVIG. Both procedures are burdensome for patients and repeat administration is usually required to obtain significant reduction in symptoms. In addition, the large volumes of intravenous fluid associated with the administration of IVIG can lead to pulmonary edema and kidney complications.

Potential benefits of our approach

We are pursuing gMG as part of our initial development strategy for two reasons. First, complement overactivity is known to contribute to the disease pathophysiology of gMG, providing a sound biological rationale for a C5-targeted intervention. Second – and most importantly – our proprietary market research suggests that significant unmet need exists for more patient-friendly treatment options, which we believe could be addressed by RLYB116 as a once-weekly, small volume, self-administered subcutaneous therapeutic.

PNH disease background

PNH is a rare, potentially life-threatening hematologic disease characterized by complement-mediated destruction of red blood cells, or hemolysis. Early signs of PNH include hemoglobinuria, or dark colored urine, resulting from excretion of hemoglobin from lysed red blood cells, which is more prominent in the morning and decreases during the day. More serious symptoms of PNH include anemia, excessive weakness, fatigue, severe abdominal pain, severe headaches and recurrent infections. PNH leads to over a 60-fold increase in the risk of venous thromboembolism compared to the general population and these thrombotic events lead to between 40% and 67% of deaths in PNH patients. Approximately two thirds of patients with PNH develop chronic kidney disease ("CKD"), and kidney failure is the cause of death in 8% to 18% of patients with PNH. In the absence of disease-modifying treatment, PNH results in the death of approximately 35% of affected individuals within five years of diagnosis. The prevalence of PNH has been estimated to be approximately 12-13 people per million.

Current treatments for PNH and their limitations

The only curative treatment currently available for PNH is a stem cell transplant from a related donor. However, this procedure is associated with significant risk and is typically used only in those patients with severe disease, such as life-threatening thrombosis or dangerously low blood counts. Various supportive therapies include anticoagulants, red blood cell transfusions and supplements of iron and folate. These therapies provide some relief from symptoms but do not address the underlying cause of the disease.

There are currently four approved disease-modifying drugs for PNH. Although these drugs have meaningfully improved the lives of patients with PNH, they have limitations including sub-optimal delivery (three of the four are delivered intravenously or via subcutaneous infusion) and high cost that result in limitations on access to therapy. Despite these limitations, worldwide sales of these drugs exceeded $5 billion in 2022. We believe that a product that works through a similar mechanism but with weekly dosing and a low-volume, convenient route of administration and improved patient access has the opportunity to further transform PNH therapy for patients.

Potential benefits of our approach

We believe PNH represents an attractive development opportunity for RLYB116 for several reasons. First, PNH has a well-understood disease pathophysiology driven by complement, providing a sound biological

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rationale for a C5-targeted intervention. Second, PNH offers the opportunity for early clinical validation using objective endpoints, including impact on lactate dehydrogenase, a component of red blood cells that is increased in circulation as a result of hemolysis. And third – and most importantly – we believe that with a patient-friendly and accessible therapy, RLYB116 could potentially provide transformative therapeutic impact for unserved and underserved patients with PNH globally.

Our solution: RLYB116

RLYB116 is an engineered protein that includes an Affibody molecule and an albumin binding domain. We acquired rights to RLYB116 from Swedish Orphan Biovitrum AB (Publ) ("Sobi"). RLYB116 was designed for optimal C5 binding, increased stability, as well as a long half-life in serum. Potential benefits of RLYB116 include:

•Subcutaneous administration. The low molecular weight allows for a higher concentration of active molecules than antibodiesin an equivalent volume. This increases the probability of being able to deliver RLYB116 in a volume suitable for subcutaneous administration.

•Efficiency of manufacturing. RLYB116 is expressed in E coli, providing for a more streamlined and potentially lower cost manufacturing process compared to antibodies or other biologics expressed in mammalian cell culture, which typically require larger scale and longer manufacturing times.

•Less frequent dosing. Linkage of the Affibody domain to an albumin binding domain may lengthen the dosing interval ofRLYB116 by extending the biological half-life.

•Potentially lower risk of treatment conversion. Due to 1:1 binding to C5, there is an expected lack of risk for drug-target-drugcomplex formation when switching from treatment with an antibody.

•Favorable stability. The Affibody platform provides the possibility of delivering highly stable and soluble therapeutic agents thatallow for high-concentration low-volume products.

Affibody Scaffold and RLYB116 Structure

Clinical development of RLYB116

We have completed a Phase 1 clinical trial in healthy participants that included the study of RLYB116 as a SAD and a MAD.

The SAD design was a single-blind, placebo-controlled, dose escalation trial investigating the safety, PK and PD of single dose RLYB116 in healthy participants. The SAD portion of the Phase 1 trial included five sequential ascending dose cohorts with doses ranging from 2mg up to 300mg, each enrolling 8 subjects (6 treated with RLYB116 and 2 with placebo) with a 10 week post-treatment / safety follow-up period. An overview of the clinical trial’s design is illustrated below.

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Design of the Phase 1 Clinical Trial of RLYB116 in Healthy Participants (Single Ascending Dose)

Data from the SAD portion of the trial showed consistent increases in exposure with increasing dose levels, low inter-subject variability, and a mean elimination half-life greater than 300 hours after a single SC, low volume injection. In the 100 mg dose group study participants that received RLYB116 (n=6) had a reduction in free C5 greater than 99% within 24 hours of dosing and RLYB116 was observed to be generally well-tolerated at this dose, with mild adverse events and no drug-related serious adverse events reported. Based on the data from the 100 mg dose and the volume of administration of the 300 mg dose, we elected to proceed with the 100 mg dose to initially evaluate multiple dose administration of RLYB116. Across the five single dose cohorts, adverse events were generally mild to moderate in severity with a dose-related increase in the frequency of gastrointestinal adverse events. There were no drug-related serious adverse events.

The MAD portion of the Phase 1 trial included an adaptive single-blind design with a 4-week treatment duration to evaluate the safety, tolerability, PK, and PD of RLYB116 with multiple dose SC administration. The MAD portion of the trial included four cohorts: Cohort 1 (weekly dosing of 100 mg), Cohort 2 (3 doses of 100 mg the first week followed by weekly dosing), Cohort 3 (150 mg weekly dosing reduced to 125 mg weekly dosing) and Cohort 4 (75 mg twice the first week followed by 100 mg twice per week) with post-treatment / study follow-up for 10 weeks.

Design of the Phase 1 Clinical Trial of RLYB116 in Healthy Participants (Multiple Ascending Dose)

In December 2023, we reported data from the MAD portion of the Phase 1 trial that demonstrated a 100 mg low volume (1 mL) once-weekly dose of subcutaneously administered RLYB116 achieved sustained mean reductions in free C5 of greater than 93%, including at day 29 with measurement prior to the last dose. The reduction in free C5 at 24 hours after the first dose of 100 mg was greater than 99%. In the MAD portion of the Phase 1 trial, RLYB116 also demonstrated low inter-subject variability and consistent increases in exposure

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relative to dose with a mean estimated elimination half-life for RLYB116 of >300 hours. RLYB116 administered as a 100 mg once-weekly dose was also observed to be generally well tolerated. Across the MAD portion of the trial, injection site reaction (ISR) was the most common adverse event (all mild in severity) and gastrointestinal adverse events increased with increasing dose. There was one case of severe liver function test ("LFT") elevation in Cohort 3 in a participant with a history of hepatitis that resulted in discontinuation of treatment. Finally, the measurement of anti-drug antibody ("ADA") formation in the study did not demonstrate an effect on PK or PD parameters and did not appear to be associated with an effect on the severity or incidence of adverse events.

In December 2023, we announced that we would not immediately initiate a Phase 2 clinical trial of RLYB116 for the treatment of gMG, and would prioritize near-term program investments in the RLYB116 manufacturing process. We expect that the additional manufacturing work will improve tolerability at higher doses with a low injection volume and infrequent SC administration, which will enable higher exposure to RLYB116 and potentially increase C5 reduction. If successful, we believe the anticipated manufacturing enhancements will expand the opportunity to treat a broader range of complement-mediated diseases, including PNH and antiphospholipid syndrome. Based on market research conducted to date, we believe that an effective, once-weekly, well-tolerated therapy that can be rapidly self-administered with an autoinjector would be an attractive alternative for patients suffering from gMG and other complement mediated diseases.

RLYB114 for the treatment of ophthalmic disorders

RLYB114 is a C5-targeted Affibody molecule conjugated to polyethylene glycol ("PEG"). The addition of PEG to protein therapeutics is a well-established method of extending the half-life and reducing the immunogenicity of molecules in the body. Given the role of the complement system in retinal and ocular pathology, we believe that RLYB114 could be used to treat ophthalmic diseases, including inflammatory and degenerative disorders.

Potential role of complement in ocular diseases

Dysregulation of the complement system may drive ocular inflammation and contribute to vision loss in multiple diseases such as age-related macular degeneration ("AMD"). A number of genetic studies have shown links between alterations in genes encoding various complement factors and the risk of development of AMD. Several clinical trials of inhibitors of the complement pathway including C5 inhibitors have been conducted, with reports of modest efficacy. Reasons for this limited efficacy are unknown but could include the disease stage, level of intervention in the complement pathway, drug delivery mechanism and the ability of the therapeutic to cross Bruch’s membrane and the retinal pigment epithelium.

Our solution: RLYB114

In February 2023, we entered into a collaboration with EyePoint. We are evaluating RLYB114 with EyePoint’s proprietary technology for sustained intraocular drug delivery, with the initial focus on geographic atrophy, an advanced form of age-related macular degeneration that leads to irreversible vision loss. We and EyePoint expect to provide an update on this collaboration in the first half of 2024.

RLYB331 for the treatment of severe anemia with ineffective erythropoiesis and iron overload

In May 2022, we obtained worldwide exclusive rights to RLYB331, a preclinical antibody. We believe RLYB331 has the potential to address a significant unmet need for patients with severe anemias with ineffective erythropoiesis and iron overload, including beta thalassemia and a subset of lower risk myelodysplastic syndromes. Currently these patients are underserved by the existing standard of care.

RLYB331 is a monoclonal antibody that is designed to inhibit MTP-2. The inhibition of MTP-2 significantly increases levels of hepcidin, decreases iron load and treats ineffective erythropoiesis. We are continuing with preclinical activities to support the transition of this asset into clinical development and expect to report additional animal data from this program in the first half of 2024.

AI drug discovery collaboration with Exscientia

We established a partnership with Exscientia, an AI and machine learning drug discovery company. Our partnership currently consists of a joint venture that is focused on the discovery and development of small molecules for the treatment of patients with rare metabolic diseases. We are initially targeting ENPP1, an

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enzyme involved in regulating extracellular levels of pyrophosphate, a natural inhibitor of calcium mineralization in bone formation, for the treatment of patients with HPP.

RE Ventures I, LLC : ENPP1 inhibitor program for the treatment of patients with HPP

We are developing an ENPP1 inhibitor for the treatment of patients with HPP, a rare, potentially life-threatening genetic disease characterized by mutations in the ALPL gene. These mutations lead to diminished activity of the tissue non-specific alkaline phosphatase ("TNSALP") enzyme and the accumulation of PPi, which inhibits bone mineralization causing multiple skeletal pathologies. ENPP1 is a Type II transmembrane glycoprotein that cleaves ATP, producing PPi, and is a major source of PPi production in cells. We believe that controlling inhibition of ENPP1 may reduce PPi levels and restore balance within the bone mineralization process.

HPP disease overview

HPP is an inherited disorder that affects the development of bones and teeth. The most severe forms of the disorder tend to occur before birth and in early infancy. Infants afflicted with the disorder have short limbs, an abnormally shaped chest, soft skull bones, poor feeding, failure to gain weight, respiratory complications and high levels of calcium in the blood, or hypercalcemia, which can lead to life-threatening complications. In other cases, the disease is not recognized until later in childhood where it manifests as rickets, pain, decreased mobility, deficits of growth and fractures. Children with less severe HPP can experience early loss of primary teeth and may have short stature with bowed legs or knock knees, enlarged wrist and ankle joints and an abnormal skull shape. Findings in adults include a softening of the bones, known as osteomalacia, and recurrent fractures in the foot and thigh bones that can lead to chronic pain. The incidence of HPP has been reported to be 1 in 100,000 (United States and Canada) to 1 in 300,000 (EU) for severe disease and 1 in 6,370 (EU) for less severe forms.

The various manifestations of HPP are caused by the combination of a lack of phosphate and an excess of PPi due to a deficiency of TNSALP, the enzyme that converts PPi to phosphate. This deficiency negatively impacts bone formation by reducing the hydrolysis of PPi to phosphate required for normal bone formation, resulting in a build-up of PPi, a potent inhibitor of mineralization.

Strensiq, an enzyme replacement therapy marketed by AstraZeneca plc ("AstraZeneca"), is the only approved therapy to treat patients with perinatal-, infantile-and juvenile-onset HPP. The therapy has been shown to lead to significant improvements in morbidity and mortality in patients with perinatal- and infantile-onset HPP, and improvements in morbidity for patients with juvenile-onset HPP. However, Strensiq has limitations, including its dosing regimen and patient access. Strensiq is administered by subcutaneous injection either three or six times per week using a weight-based dosing scale, which can be both onerous and painful for patients.

Our solution: an ENPP1 small molecule inhibitor

We are developing an orally available, small molecule ENPP1 inhibitor designed to reduce PPi levels through the controlled inhibition of ENPP1, which we hypothesize may restore the balance of PPi and phosphate needed to promote bone mineralization. We and Exscientia expect to select a small molecule development candidate to advance into clinical development. Proof of mechanism studies are in progress with a leading global HPP expert. We plan to provide an update on the progress of the program in the second half of 2024.

Scientific Rational: ENPP1 Inhibition for the Treatment of Hypophosphatasia

Under normal conditions, the level of PPi and Pi is kept in balance by activity of TNSALP, ENPP1 and ANKH. In patients with HPP, the reduction of PPi hydrolysis by TNSALP results in a relative increase in PPi, leading to an inhibition of mineralization, and inhibited hydroxyapatite formation.

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Through controlled inhibition of ENPP1, we aim to reduce PPi and improve mineralization, restoring hydroxyapatite formation.

AbCellera Collaboration

We entered into a strategic alliance with AbCellera to discover, develop, and commercialize novel antibody-based therapeutics for rare diseases. This multi-year, multi-target collaboration combines AbCellera’s antibody discovery engine with Rallybio’s clinical and commercial expertise in rare diseases to identify optimal clinical candidates with a goal of delivering therapies to patients. AbCellera and Rallybio intend to co-develop up to five rare disease therapeutic targets, which will be chosen together by both companies. The partnership’s first program is focused on addressing the significant unmet therapeutic needs of patients with rare metabolic diseases.

Competition

The biotechnology and pharmaceutical industries are highly competitive and subject to significant and rapid technological change. There are many public and private biopharmaceutical companies, universities, government agencies and other research organizations actively engaged in the research and development of products that may be like our product candidates or address similar markets. In addition, the number of companies seeking to develop and commercialize products and therapies competing with our product candidates is likely to increase. However, we seek to build our portfolio with key differentiating attributes to provide a competitive advantage in the markets we target. The success of our product candidates, if approved, is likely to be a result of their efficacy, safety, convenience, price, the level of biosimilar or generic competition and/or the availability of reimbursement from government and other third-party payors.

FNAIT. There are currently no approved therapies for the prevention or treatment of FNAIT. In one frequently used approach to managepregnancies where the mother is known to have a history of FNAIT, physicians administer high levels of IVIG. Companies that currently market IVIG include ADMA Biologics, Bio Products Laboratory, CSL Behring, Grifols, Kedrion Biopharma, Leadiant Biosciences, Octapharma and Takeda Pharmaceutical Company Limited.

gMG. Very early-stage gMG is symptomatically treated by the use of acetylcholinesterase inhibitors such as pyridostigmine bromide, marketedas Mestinon by Bausch Health. Eculizumab and ravulizumab are also approved for the treatment of gMG in patients who are positive for anti-AChR antibodies. Efgartigimod, marketed as Vyvgart by Argenx SE, is a neonatal Fc receptor blocker also approved for the treatment of patients with generalized MG who are positive for anti-AChR antibodies and Zilbrysq, a macrocyclic peptide marketed by UCB Pharma was approved for the treatment of AChR+ adult patients with gMG. Rozanolixizumab, marketed as Rystiggo by UCB, is a neonatal Fc receptor blocker approved for the treatment of gMG in adult patients who are AChR+ or anti-MuSK antibody positive. There are several other companies developing assets in mid- to late-stage clinical development for the treatment of gMG using a variety of approaches and modalities. These companies include AstraZeneca, Horizon Therapeutics (acquired by Amgen Inc.) and Immunovant, Inc.

PNH. The only curative treatment currently available for PNH is a stem cell transplant from a related donor. However, this procedure isassociated with significant risk and is used only in those patients with severe disease, such as life-threatening thrombosis or dangerously low blood counts. Various supportive therapies include anticoagulants, red blood cell transfusions and iron and folate supplements. These therapies provide some relief from symptoms but do not address the underlying cause of the disease. There are four approved

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drugs for PNH: eculizumab, marketed by AstraZeneca as Soliris; ravulizumab, marketed by AstraZeneca as Ultomiris; pegcetacoplan, marketed by Apellis Pharmaceuticals as Empaveli, and iptacopan, marketed by Novartis AG as Fabhalta. Eculizumab and ravulizumab are antibodies that bind complement C5; pegcetacoplan is a pegylated pentadecapeptide that targets complement C3; and iptacopan is a small molecule that inhibits complement factor B. There are several companies in mid- to late-stage clinical trials developing treatments for PNH. These include Roche, AstraZeneca, and Alnylam Pharmaceuticals, Inc. among others.

HPP. There is one approved treatment for HPP, asfotase alfa, marketed by AstraZeneca as Strensiq, which is an alkaline phosphotase enzyme replacement therapy, and the only approved therapy for the treatment of perinatal-, infantile- and juvenile-onset HPP. AstraZeneca is developing a second generation enzyme replacement therapy, ALXN-1850 which is currently in clinical development, and Aruvant is developing ARU-2801, an AAV gene therapy currently in preclinical development. There are several companies pursuing ENPP1 small molecule inhibitors for the treatment of cancer, including Angarus Therapeutics, Avammune Therapeutics, Tcino Bioscience, Nanjing Zenshine Pharmaceuticals Co., Ltd. and Stingray Therapeutics, Inc. with all these companies in discovery or preclinical development. We are not aware of other small molecule inhibitors in development for the treatment of patients with HPP.

Many of our competitors may have significantly greater name recognition and financial, manufacturing, marketing, product development, technical, commercial infrastructure, and human resources than we do. Mergers and acquisitions in the pharmaceutical, biotechnology and diagnostic industries may result in even more resources being concentrated among a smaller number of our competitors. These competitors also compete with us in establishing clinical trial sites and patient registration for clinical trials, as well as in acquiring technologies complementary to, or necessary for, our programs. Smaller or early-stage companies may also prove to be significant competitors, particularly through collaborative arrangements with large and established companies.

Intellectual Property

Our success depends, in part, on our ability to obtain, maintain, defend, and enforce patent rights and other intellectual property rights that protect our business, preserve the confidentiality of our trade secrets, and operate without infringing the valid and enforceable intellectual property rights of others. In addition to our efforts to protect our product candidates and methods of using them, we also seek to secure or acquire patent rights regarding other products and methods that are important to the general development of commercial products. We utilize a multi-layered approach that includes acquiring intellectual property rights through purchase or exclusive license, filing and prosecuting U.S. and foreign patent applications directed to our own innovations, and developing and protecting proprietary know-how to maintain our competitive position.

Our ongoing efforts to secure patent rights that protect our business constitute a key component of our business strategy. We also strive to protect as trade secrets or confidential know-how, certain aspects of our programs and technological innovations that are commercially valuable but are not amenable to or appropriate for patent protection. We achieve this, in part, through the use of confidentiality agreements with our employees, consultants, scientific advisors, collaborators, licensors, and contractors, and by striving to maintain physical security of our premises and digital security of our electronic information and technology systems.

Notwithstanding our commitment to protecting our intellectual property rights, we, like other pharmaceutical and biopharmaceutical companies, are subject to several sources of uncertainty that can affect those rights. For example, we cannot be certain that any patents that we currently own or in-license, or that we may own or in-license in the future, will not be challenged, held to be invalid and/or unenforceable, have the scope of their claims narrowed, or be circumvented by others. Nor can we be certain that such patents will successfully protect our products or our business from competition.

Similarly, with respect to patent applications that are currently pending, or that may be pending in the future, we cannot be certain that such patent applications will result in the issuance of granted patents, or of patent claims with the desired claim scope. In order to secure an issued patent, an invention claimed in a patent application must meet certain legal requirements for patentability, which differ between countries based on each country’s particular patent laws. In addition, because of the significant amount of time required for clinical development and regulatory review of product candidates, we cannot be certain that any of our product candidates will be commercialized while there is significant patent term remaining on patents relating to those products. The term of a patent depends upon the legal requirements for determination of patent term in the

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country in which that patent is granted. In most countries, including the United States, the patent term is 20 years from the earliest claimed filing date of a non-provisional patent application. In the United States, a patent’s term may, in certain cases, be lengthened by patent term adjustment ("PTA") which compensates a patentee for administrative delays by the U.S. Patent and Trademark Office ("USPTO") in examining and granting the patent. Likewise, a patent’s term may be shortened if it is terminally disclaimed over an earlier-expiring patent with a common owner or inventor.

The term of a U.S. patent relating to an approved drug product may also be extended to compensate the patentee for delays due to the regulatory approval process. Such a patent term extension ("PTE") cannot exceed five years, and cannot extend the remaining term of a patent beyond a total of 14 years from the date of product approval. Furthermore, the term can be extended for only one patent applicable to each regulatory review period and only those claims covering the approved product, or a method for using it or manufacturing it, may be extended. In the future, if any of our product candidates receive approval by the FDA we expect to apply for PTE on any issued patents covering those products, depending upon the length of the clinical studies for each product and other factors. There can be no assurance that we will benefit from any PTE or favorable adjustments to the terms of any patents we currently own or in-license or that we may own or in-license in the future.

In addition to and separate from patent exclusivity, the FDA may also grant marketing exclusivity of varying lengths in connection with the approval of a New Chemical Entity (5 years), Biologic (12 years), or Orphan Drug indication (7 years). Marketing exclusivity may also be granted for new clinical studies (3 years) and pediatric studies (6 months) on approved drugs. Depending on the length of the regulatory approval process and the ability to make use of the procedures for obtaining PTE, any FDA exclusivity period may in part or in whole overlap with any patent exclusivity to which we are entitled. We intend to pursue relevant marketing exclusivities in the US and in foreign countries in which any candidate product is approved. However, we cannot be certain that any such exclusivities will be granted or, if granted, will insulate our commercial product(s) from competition.

With respect to trade secrets, while we have confidence in the protective measures that we employ, such measures can be breached, and we may not have adequate remedies for any such breach. We also cannot be certain that any of our activities will not be subject to the intellectual property rights of others.

As of March 1, 2024, we owned two patent families that were acquired from Prophylix AS ("Prophylix") and relate to the current product candidates in our FNAIT prevention program, RLYB211 and RLYB212. The acquired patent family covering RLYB212 and its use in treating and preventing FNAIT includes patents issued or accepted in Australia, Canada, Europe, Israel, Mexico, New Zealand, Russia, and the United States. A patent application in this family is pending in Brazil. The granted patents in this family will expire in 2035, excluding any PTA or PTE that may be awarded. The acquired patent family covering administration of RLYB211 for the prophylactic treatment of FNAIT includes patents issued in the United States, Europe and Canada. The foreign patents and one of the U.S. patents will expire at the end of 2026, while the other U.S. patent expires in November 2030 due to a PTA granted by the USPTO. We own three patent families directed to dosing and administration of RLYB212.Two of these families each include patent applications pending in Australia, Canada, Europe, Israel, Mexico, New Zealand, and the United States. Patents issuing in these two families will have an expiration date of June 2042, excluding any PTA or PTE that may be awarded. The third family is a pending United States provisional patent application. In addition, we filed and own two pending International (PCT) patent applications, one directed to assays for quantifying anti-HPA1a antibodies and the other directed to the formulation of RLYB212. We also exclusively in-license certain rights to technology from Versiti Blood Research Institute Foundation, Inc. pertaining to a mouse model of FNAIT.

As of March 1, 2024, we owned two patent families relating to the current product candidates in our complement program, RLYB114 and RLYB116, and certain aspects of their use that were acquired from Sobi. These two patent families currently include four granted U.S. patents and one pending U.S. patent application, with granted patents and/or pending patent applications in more than 25 additional countries worldwide. In the United States, Australia, Canada the European Patent Convention contracting states, and Japan, applications in both patent families have been granted and are scheduled to expire between 2033 and 2034, excluding any PTA or PTE. In addition, we filed and own a pending International (PCT) patent application directed to dosing and administration of RLYB116, and six pending provisional patent applications directed to methods of treatment of various C5-related conditions by administration of RLYB116. We have also non-exclusively in-licensed certain

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patent rights relating to our current product candidates from Affibody, including patent rights relating to the Affibody molecule technology and Albumod albumin binding molecule technology.

As of March 1, 2024, we exclusively in-licensed from Kymab Limited certain patent rights to the current product candidate in our iron overload program, RLYB331, as well as back-up compounds. Under the exclusive license, we are managing prosecution of a patent family relating to RLYB331 and the back-up compounds. The patent family currently includes pending patent applications in the United States and in more than 20 other countries/regions, including Australia, Brazil, Canada, China, Eurasia, Europe, India, Japan, Mexico, and Saudi Arabia. In addition, we have non-exclusively in-licensed from Kymab Limited certain patent rights relating to the development, manufacture, and use of RLYB331 and the back-up compounds.

License Agreements

Product License Agreement with Affibody AB

In March 2019, our subsidiary IPC Research, LLC ("IPC Research") and Sobi entered into a Contract Assignment Agreement pursuant to which Sobi assigned to, and IPC Research assumed, all obligations in a certain Product License Agreement ("PLA") as amended, between Sobi and Affibody AB ("Affibody"), dated March 9, 2012, as amended on January 1, 2018 and December 22, 2020.

Pursuant to the PLA, we obtained a license to the Affibody platform technology and a particular albumin binding domain ("ABD"), in order to further develop and commercialize certain Affibody ligands, which we are now developing as RLYB116 and RLYB114.

Under the PLA, Affibody grants us (1) a non-exclusive right under certain patents to use the Affibody ligands alone or as a fusion protein and (2) an exclusive right to use the Affibody ligands alone or as a fusion protein, in each case, for human therapeutic use. Affibody also grants us (a) a non-exclusive right under certain patents to use the ABD in combination with the Affibody ligands as a fusion protein and (b) an exclusive right to use the ABD solely in combination with the Affibody ligands as a fusion protein, in each case, for human therapeutic use. Affibody grants us a non-exclusive license under applicable know-how needed to practice the rights and licenses granted under the PLA. All licenses to us are sublicensable, provided that each sublicense is consistent with the terms and conditions of the PLA. Under the PLA, Affibody has an exclusive right under any product patents, which are a category of certain patents that we own, to use the specific Affibody ligands outside of human therapeutics and a non-exclusive right under know-how needed to practice the Affibody ligands outside of human therapeutics.

Under the PLA, Affibody is the exclusive owner of, and controls prosecution, maintenance, and defense of intellectual property covering, platform technology. We are the exclusive owner of, and control prosecution, maintenance, and defense of intellectual property covering, product technology. Affibody agrees to disclose to us any improvement to the Affibody technology that it deems commercially reasonable for us to practice and grants us an option to license any such improvement. We have the first right to enforce product patents against a third-party infringer and Affibody retains the first right to enforce any other licensed patent. We agree to not provide or make available any Affibody Ligand to a third-party on a standalone basis except for research purposes or to commercialize a licensed product.

We agree to use commercially reasonable efforts to develop and commercialize a licensed product. We also will pay Affibody certain regulatory milestones up to an aggregate amount of €7.5 million and (a) a mid-single-digit royalty on annual net sales of products if such products are covered by a valid claim of a product patent or a platform patent or (b) low-single-digit royalties on annual net sales of products that are not covered by any such valid claim. Our obligation to pay royalties expires on a country-by-country and product-by-product basis on the later of (a) the expiration of the last-to-expire valid claim of a patent covering a licensed product or (b) the 10th anniversary following first commercial sale of such product in such country.

The PLA will terminate when we are no longer obligated to pay royalties to Affibody. Either party may terminate the PLA upon material breach of the PLA by the other, subject to a cure period, or immediately in the case of the other party’s insolvency, bankruptcy or a similar event. Affibody may terminate the PLA immediately if we or any of our affiliates or third party transferees commences any proceeding challenging the validity of the licensed patents or any of Affibody’s other patents or challenging the confidentiality or substance of the licensed know-how or licensed technology. We may terminate the PLA for convenience upon 90 days prior written notice and upon payment of any amounts due to Affibody through the effective date of such termination.

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If Affibody terminates the PLA or if we terminate the PLA for convenience, (a) all rights and licenses granted under the PLA will terminate, (b) at Affibody’s request, we must transfer all rights to the product technology free of charge to Affibody and (c) we must return or destroy all of Affibody’s confidential information. Furthermore, if we terminate for convenience, we must grant Affibody an exclusive, royalty free perpetual right to use all regulatory filings, approvals and data provided to regulatory authorities in support of such filings or approvals that relate to the licensed product. However, if we terminate the PLA as a result of Affibody’s material breach of the PLA or its insolvency or bankruptcy, we will retain our license and rights under the PLA, provided that we will remain bound by certain obligations under the PLA with respect milestone payments, royalties (subject to a reduction in rate, in the case of material breach), audits and indemnity.

Product License Agreement with Sanofi

In May 2022, through our subsidiary, Rallybio IPE, LLC ("Rallybio IPE"), we entered into a License Agreement with Kymab Limited ("Sanofi", and such agreement the "Sanofi License Agreement"). Under the Sanofi License Agreement, Sanofi provides Rallybio IPE with worldwide exclusive rights to Sanofi’s KY1066, which is now referred to as RLYB331. Under the terms of the Sanofi License Agreement, Rallybio has an exclusive license to certain Sanofi patents to develop, manufacture and commercialize RLYB331 and Rallybio agrees to use commercially reasonable efforts to develop and commercialize a licensed product in at least one indication in the field in each of several major markets, as described in the Sanofi License Agreement.

We paid Sanofi an upfront cash payment of $3.0 million. In addition, Rallybio has agreed to pay Sanofi up to an aggregate of $43.0 million in development and regulatory milestones and up to an aggregate of $150.0 million in commercial milestones for a product in its first indication, plus tiered low-to-mid double digit percentages of such milestone amounts for up to three additional indications, and mid to high single digit royalties on net sales.

The Sanofi License Agreement contains other customary license terms including sublicensing, development, regulatory, manufacturing, commercialization, milestones, royalties, intellectual property, and termination. The Sanofi License Agreement will expire on a product-by-product and country-by-country basis at the end of the applicable royalty term. Either party may terminate the Sanofi License Agreement upon material breach of the Sanofi License Agreement by the other, subject to a cure period. Rallybio may terminate the Sanofi License Agreement for convenience upon 90 days prior written notice to Sanofi. Sanofi may terminate the Sanofi License Agreement immediately in the case of Rallybio’s insolvency, bankruptcy or a similar event, or if Rallybio or its affiliates participates in any proceeding challenging the validity of the licensed patents.

If the Sanofi License Agreement is terminated in its entirety, among other things (a) all rights and licenses granted by Sanofi under the License Agreement (including any sublicenses) will terminate and (b) if Sanofi has an interest in developing, manufacturing and commercializing the licensed compounds or products, the parties to the Sanofi License Agreement shall negotiate an arrangement to provide Sanofi rights to the patents, know-how, materials and other properties controlled by Rallybio applicable to any of the licensed product.

Asset Purchase Agreements

Asset Transfer Agreement with Swedish Orphan Biovitrum AB (Publ)

In March 2019, through IPC Research, we entered into an agreement with Sobi, pursuant to which we acquired the right, title and interest in assets related to certain C5 inhibitor compounds. We are currently developing the assets acquired from Sobi as RLYB116 and RLYB114.

We paid Sobi an upfront purchase price of $5.0 million and we are obligated to pay Sobi an aggregate amount of up to $51.0 million upon achievement of certain development milestones and an aggregate amount of up to $65.0 million upon achievement of certain sales milestones.

We also will pay Sobi tiered, low single-digit royalties on annual net sales to third parties for products containing any compound transferred under the agreement as an active ingredient. Our obligation to pay royalties expires, on a country-by-country and product-by-product basis, on the later of (a) the 10th anniversary following first commercial sale of such product in such country and (b) the expiration date in such country of the last to expire of any issued patent included in the patent rights acquired from Sobi that includes at least one valid claim covering the sale of such product in such country.

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We are obligated to use commercially reasonable efforts to research, develop and exploit at least one product that contains a compound transferred under the agreement as an active ingredient in each of the United States, EU and Japan.

If, prior to the commercial launch in the United States of the first product containing the compounds, we decide to divest our rights in the assets acquired from Sobi or to terminate all research, development and commercialization activities in respect of the acquired compounds, we must notify Sobi and negotiate in good faith with Sobi a possible business transaction relating to the assets. This right of negotiation will not apply to a transaction to sell all or substantially all of the assets of IPC Research or an affiliate of IPC Research, a pledge of the assets as collateral or a sale or transfer of the assets to an affiliate of IPC Research that agrees to be bound by the right of negotiation.

Asset Purchase Agreement with Prophylix

In June 2019, though our subsidiary Rallybio IPA, LLC ("Rallybio IPA"), we entered into an agreement with Prophylix to acquire all of Prophylix’s rights, title and interest in, to and under all assets, properties and rights related to Prophylix’s plasma-derived anti-HPA-1a immunoglobulin, and Prophylix’s monoclonal antibody, which we are developing as RLYB212.

We paid Prophylix an upfront purchase price of approximately $1.2 million and reimbursed Prophylix approximately $1.8 million for certain manufacturing costs incurred by Prophylix. We are obligated to pay Prophylix an aggregate of up to $ 19.0 million upon achievement of certain development milestones and an aggregate of up to $20.0 million upon achievement of certain sales milestones.

We also will pay Prophylix tiered, mid-single-digit royalties on annual net sales of products containing the monoclonal antibody and tiered mid-to-high-single and low-double-digit royalties on annual net sales of products containing plasma-derived anti-HPA-1a immunoglobulin, subject to certain offsets for royalties payable under certain third-party licenses. Furthermore, the then-applicable royalty rate will be reduced by a mid-double digit percentage for the remaining royalty term on a country-by-country basis if it becomes reasonably likely that the Prophylix patents may no longer be enforceable in such country due to a challenge of the enforceability of the patents or the enforceability of the royalty payments following the expiration of all valid claims of the patents in such country. Our obligation to pay royalties terminates on a country-by-country and product-by-product basis on the later of (a) the expiration of the last-to-expire valid claim of a Prophylix patent covering a product, (b) expiration of regulatory exclusivity for the product in such country or (c) the 10th year anniversary following first commercial sale of such product in such country.

In the event the FDA grants a priority review voucher for one of our product candidates developed using the technology acquired from Prophylix, we will pay Prophylix either: (a) if we sell such priority review voucher to a third-party within 12 months of its receipt, a mid-double digit percentage of the proceeds we receive from the sale, net of taxes, or (b) if we do not sell the priority review voucher to a third-party within 12 months of receipt, a mid-double digit percentage of the fair market value of the priority review voucher as determined in accordance with the agreement.

We are obligated to use commercially reasonable efforts to develop and commercialize products containing plasma-derived anti-HPA-1a immunoglobulin in the United States and in at least one major European market. The agreement provides that if we provide notice to Prophylix that we determined that commercialization of products containing plasma-derived anti-HPA-1a immunoglobulin is not feasible due to an insufficient plasma supply following our continued and diligent efforts to obtain a sufficient plasma supply, then our obligation to develop products containing plasma-derived anti-HPA-1a immunoglobulin will cease, and we will be obligated to use commercially reasonable efforts to develop and commercialize products containing the monoclonal antibody in the United States and in at least one major European market.

If, after using commercially reasonable efforts to develop and commercialize products containing plasma-derived anti-HPA-1a immunoglobulin and the monoclonal antibody in the United States and in at least one major European market, we decide not to pursue any further development or commercialization activities for such products, then Prophylix will have the right to repurchase the remaining assets acquired under the agreement for approximately $1.2 million. Prophylix also will have the right to repurchase the remaining assets acquired under the agreement for approximately $1.2 million if we elect to transfer all or substantially all of the

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assets acquired under the agreement to a third-party who does not agree to assume our obligations to develop and commercialize the products.

Joint Venture Agreement

In July 2019, we entered into a partnership with Exscientia and created RE Ventures I, LLC ("RE Ventures"), which is jointly owned by Exscientia and one of our wholly-owned subsidiaries, each a Member and collectively the Members. The joint venture was formed to initiate early-stage drug discovery of orally available small molecules targeting ENPP1 for the treatment of HPP, and thereafter for the future research, development, manufacture, sale and exploitation of any company-owned technology and compounds, including any resulting compound identified by the steering committee of the joint venture.

Under the RE Ventures operating agreement, we received a 50% interest in the joint venture in exchange for an initial contribution of £0.5 million ($0.6 million, based on the exchange rate at the time). RE Ventures used this initial capital to fund stage 1 of the ENPP1 program, and we committed to fund additional amounts if costs of stage 1 exceeded the initial funding. In June 2020, RE Ventures determined that the stage 1 objective of discovering compounds for ENPP1 with a certain potency had been achieved. In 2020, we contributed £ 1.1 million ($1.3 million, based on the exchange rate at the time) and in 2021, we contributed approximately £1.4 million ($2.0 million, based on the exchange rate at the time) to RE Ventures in support of ongoing Stage 2 development of the ENPP1 program. In 2022, we contributed £0.2 million ($0.3 million, based on the exchange rate at the time) and in 2023, we contributed £1.8 million ($2.3 million, based on the exchange rate at the time) to RE Ventures in support of ongoing development of the ENPP1 program. The board of managers of RE Ventures may determine from time to time that additional capital is necessary or appropriate to enable RE Ventures to conduct its activities, and may seek (but not require) additional capital contributions from the Members.

In the event that either Member does not fund a portion of committed additional amounts, the other Member may contribute the unfunded amount and the respective membership interests in RE Ventures will be adjusted accordingly.

A steering committee is responsible for oversight of RE Ventures’ research and deployment plans as well as intellectual property and regulatory matters. A two-person board of managers manages the business and affairs of RE Ventures and is responsible for all management and other responsibilities not specifically reserved to the steering committee or to the Members. Each Member designates one member to the board.

Each Member is subject to customary restrictions on its transfer of interests in RE Ventures, including a right of first refusal, co-sale right and drag-along provision.

AbCellera Collaboration Agreement

In December 2022, the Company entered into a strategic alliance to discover, develop, and commercialize novel antibody-based therapeutics for rare diseases. This multi-year, multi-target collaboration will combine AbCellera’s antibody discovery engine with Rallybio’s clinical and commercial expertise in rare diseases to identify optimal clinical candidates and ultimately deliver therapies to patients.

Under the terms of the agreement, AbCellera and Rallybio will co-develop up to five rare disease therapeutic targets, which will be chosen together by both companies. The collaboration will allow Rallybio to add product candidates to its existing pipeline and also provides the option for AbCellera to conduct process development and clinical manufacturing activities. The partnership’s first program will focus on addressing the significant unmet therapeutic needs of patients with rare metabolic diseases.

Manufacturing and Supply

We do not own or operate, and currently have no plans to establish, any internal manufacturing facilities. We currently rely and expect to continue to rely on third-party contract manufacturer organizations ("CMOs") for the manufacture of our product candidates for preclinical and clinical testing, as well as for commercial production of any product candidates that are approved.

We currently rely on multiple CMOs for all of our preclinical and clinical supply requirements, including drug substances and drug products, and label and packaging for our preclinical research and clinical trials. We believe that we will be able to contract with other CMOs to manufacture drug substances if our existing sources

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of drug substances were no longer available to us or with sufficient capacity, but there is no assurance that the drug substance capacity would be available from other CMOs on acceptable terms, on the timeframe that our business would require, or at all. We do not currently have supply commitments or other arrangements in place with our existing CMOs.

We do not have any current contractual relationships for the manufacture of commercial supplies of any of our product candidates if they are approved by the regulatory authorities, and we intend to enter into agreements with a CMO and one or more back-up manufacturers for the commercial production of our product candidates as they near phase 3 clinical trials.

Any products to be used in clinical trials and any approved product that we may commercialize will need to be manufactured in facilities, and by processes, that comply with the FDA’s current Good Manufacturing Practice ("cGMP") requirements and comparable requirements of the regulatory agencies of other jurisdictions in which we are seeking approval. We currently employ internal resources to manage our CMOs. We believe that RLYB212, RLYB116, RLYB114, and RLYB331 can be manufactured through reliable and reproducible biologic and chemical processes from readily available starting materials. We believe that our manufacturing processes are amenable to scale-up and will not require unusual or expensive equipment. We expect to continue to develop, on our own or with our collaborators, product candidates that can be produced cost-effectively at contract manufacturing facilities.

We expect to rely on third parties for the manufacture of any in vitro diagnostic device, companion diagnostics or companion drug delivery systems we develop. For example, we have engaged a third-party to assist in developing laboratory screening tests and in our evaluation of potential companion diagnostics in conjunction with our development of RLYB212. Depending on the regulatory pathway and technology solutions we choose, we may engage third parties to continue the development and manufacturing of any device developed to support our therapeutic products.

Government Regulation

The research, development, testing, manufacture, quality control, packaging, labeling, storage, record-keeping, distribution, import, export, promotion, advertising, marketing, sale, pricing and reimbursement of drug and biologic products are extensively regulated by governmental authorities in the United States and other countries. The processes for obtaining regulatory approvals in the United States and in foreign countries and jurisdictions, along with compliance with applicable statutes and regulations and other regulatory requirements, both pre-approval and post-approval, require the expenditure of substantial time and financial resources. The regulatory requirements applicable to drug and biological product development, approval and marketing are subject to change, and regulations and administrative guidance often are revised or reinterpreted by the agencies in ways that may have a significant impact on our business.

U.S. Government Regulation of Drug and Biological Products

In the United States, the FDA regulates human drugs under the Federal Food, Drug, and Cosmetic Act, (the "FDCA"), and in the case of biologics, also under the Public Health Service Act (the "PHSA"), and their implementing regulations. Failure to comply with the applicable U.S. requirements may result in FDA refusal to approve pending New Drug Applications ("NDAs") or Biologics License Applications ("BLAs") or delays in development and may subject an applicant to administrative or judicial sanctions, such as issuance of warning letters, or the imposition of fines, civil penalties, product recalls, product seizures, total or partial suspension of production or distribution, injunctions and/or civil or criminal prosecution brought by the FDA and the U.S. Department of Justice or other governmental entities.

The FDA must approve our product candidates for therapeutic indications before they may be marketed in the United States. For drug products, the FDA must approve an NDA, and for biologic products, the FDA must approve a BLA. An applicant seeking approval to market and distribute a new drug or biologic in the United States generally must satisfactorily complete each of the following steps:

•completion of preclinical laboratory tests and animal studies according to Good Laboratory Practice ("GLP") regulations or other applicable regulations;

•manufacture and testing of the therapeutic or biologic moiety and its respective product formulation according to cGMP regulations or other applicable regulations;

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•submission to the FDA of an investigational new drug application ("IND"), which must become effective before human clinical trials may begin and must be updated annually and amended when certain changes are made;

•approval by an independent institutional review board ("IRB") or ethics committee representing each clinical trial site before each clinical trial may be initiated;

•performance of adequate and well-controlled human clinical trials in accordance with applicable IND regulations, good clinical practices ("GCPs") and other clinical-trial related regulations to evaluate the safety and efficacy of the investigational product for each proposed indication;

•preparation and submission to the FDA of an NDA or BLA requesting marketing approval for one or more proposed indications, including payment of application user fees;

•review of the NDA or BLA by an FDA advisory committee, where applicable;

•satisfactory completion of one or more FDA inspections of the manufacturing facility or facilities at which the drug or biologic and its respective finished product is produced to assess compliance with cGMP requirements to assure that the facilities, methods and controls are adequate to preserve the product’s identity, strength, quality and purity;

•satisfactory completion of any FDA audits of clinical trial sites to assure compliance with GCPs and the integrity of the clinical data submitted in support of the NDA or BLA; and

•FDA review and approval of the NDA or BLA, which may be subject to additional post- approval requirements, including the potential requirement to implement a Risk Evaluation and Mitigation Strategy ("REMS") and any other potential post- approval studies required by the FDA.

Preclinical Studies and IND

Before testing any drug or biological product candidate in humans, the product candidate must undergo rigorous preclinical testing. The preclinical development stage generally involves laboratory evaluations of drug chemistry/biology, formulation, and stability, as well as in vitro and animal studies to assess safety and in some cases to establish a rationale for therapeutic use. The conduct of preclinical studies is subject to federal regulations and requirements, including GLP regulations for safety and toxicology studies. The sponsor must submit the results of the preclinical studies, together with manufacturing information, analytical data, any available clinical data or literature and a proposed clinical protocol, to the FDA as part of the IND.

An IND is a request for authorization from the FDA to administer an investigational product to humans and must become effective before human clinical trials may begin. An IND automatically becomes effective 30 days after receipt by the FDA, unless before that time, the FDA raises concerns or questions related to one or more proposed clinical trials and places the clinical trial on a clinical hold. In such a case, the IND sponsor and the FDA must resolve any outstanding concerns before the clinical trial can begin. Imposition of a clinical hold could cause significant delays or difficulties in initiating and/or completing planned clinical trials in a timely manner. Certain long-term preclinical testing, such as animal tests of reproductive adverse events and carcinogenicity, may initiate or continue after an IND for an investigational product candidate is submitted to the FDA and human clinical trials have been initiated.

Human Clinical Trials in Support of an NDA or BLA

Clinical trials involve the administration of an investigational product candidate to healthy volunteers or patients with the disease to be treated under the supervision of qualified investigators. Clinical trials are conducted under protocols detailing the objectives of the study, inclusion and exclusion criteria, dosing procedures and the parameters to be used in monitoring the safety and effectiveness criteria to be evaluated. Each protocol, as well as any subsequent amendments, must be submitted to the FDA as part of the IND.

An IRB representing each institution that is participating in the clinical trial must review and approve the plan for any clinical trial before it commences at that institution, and the IRB must thereafter conduct a continuing review of the trial. The IRB will consider, among other things, clinical trial design, patient informed consent, ethical factors and the safety of human subjects. The IRB must review and approve, among other things, the trial protocol and informed consent information to be provided to clinical trial subjects or their legal representatives and must operate in compliance with FDA regulations.

Clinical trials must also comply with extensive GCP standards intended to ensure protection of human subjects and the quality and integrity of the study data, including requirements for obtaining subjects’ informed consent. Additionally, some clinical trials are overseen by an independent group of qualified experts organized by the clinical trial sponsor, known as a data safety monitoring board or committee. This group may recommend continuation of the trial as planned, changes in trial conduct or cessation of the trial at designated checkpoints

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based on access to certain data from the study. The FDA may at any time while clinical trials are ongoing impose a partial or complete clinical hold based on concerns for patient safety and/or noncompliance with regulatory requirements. This order issued by the FDA would cause suspension of an ongoing trial until all outstanding concerns have been adequately addressed, and the FDA has notified the company that investigations may proceed.

Human clinical trials to evaluate therapeutic indications to support NDAs and BLAs for marketing approval are typically conducted in three sequential phases that may overlap or be combined:

•Phase 1: The product candidate is initially introduced into human subjects and tested for safety, dosage tolerance, absorption, metabolism, distribution, and excretion, and if possible, to gain early evidence for effectiveness. Phase 1 trials may be conducted in healthy volunteers or, in the case of some products for severe or life-threatening diseases, including many rare diseases, the initial human testing is often conducted in patients with the target disease or condition.

•Phase 2: Clinical trials are conducted in a limited patient population with a specified disease or condition to identify possible adverse effects and safety risks, to preliminarily evaluate the efficacy of the product for specific targeted diseases and to determine dosage tolerance and optimal dosage. Multiple Phase 2 clinical trials may be conducted to obtain information prior to beginning larger and more expensive Phase 3 clinical trials.

•Phase 3: Clinical trials are undertaken with an expanded patient population to further evaluate dosage, and to provide substantial evidence of clinical efficacy and safety in an expanded patient population, often at geographically dispersed clinical study sites. These studies are intended to establish the overall risk-benefit ratio of the product candidate and provide, if appropriate, an adequate basis for product labeling. These trials may include comparisons with placebo and/or other comparator treatments. The duration of treatment is often extended to mimic the actual use of a product during marketing.

Post-approval trials, sometimes referred to as Phase 4 clinical trials, may be conducted after initial marketing approval. These trials are used to gain additional experience from the treatment of patients in the intended therapeutic indication, to document a clinical benefit in the case of drugs or biologics approved under FDA’s accelerated approval regulations and to generate additional safety data regarding use of the product in a clinical setting. In certain instances, the FDA may mandate the performance of Phase 4 clinical trials as a condition of approval of an NDA or BLA. Failure to exhibit due diligence with regard to conducting Phase 4 clinical trials could result in withdrawal of approval for the product.

The FDA or the sponsor may suspend or terminate a clinical trial at any time on various grounds, including a finding that the research subjects or patients are being exposed to an unacceptable health risk. Similarly, an IRB can suspend or terminate approval of a clinical trial at its institution if the clinical trial is not being conducted in accordance with the clinical protocol, GCP or other IRB requirements or if the drug has been associated with unexpected serious harm to patients.

Information about certain clinical trials, including details of the protocol and eventually study results, also must be submitted within specific time frames to the National Institutes of Health for public dissemination on the ClinicalTrials.gov data registry. Similar requirements for posting clinical trial information in clinical trial registries exist in the EU and in other countries outside the United States.

During the development of a new drug or biological product, sponsors have the opportunity to meet with the FDA at certain points, including prior to submission of an IND, at the end of phase 2 and before submission of an NDA or BLA. These meetings can provide an opportunity for the sponsor to share information about the data gathered to date and for the FDA to provide advice on the next phase of development.

Concurrent with clinical trials, companies usually complete additional nonclinical studies and must also develop additional information about the physical characteristics of the drug or biological product and finalize a process for manufacturing the product in commercial quantities in accordance with cGMP requirements. The manufacturing process must be capable of consistently producing quality batches of the product candidate and, among other things, the manufacturer must develop methods for testing the identity, strength, quality, potency and purity of the final drug or biological product. For biological products in particular, the PHSA

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emphasizes the importance of manufacturing controls for products whose attributes cannot be precisely defined in order to help ensure safety, purity and potency.

Additionally, appropriate packaging must be selected and tested, and stability studies must be conducted to demonstrate that the product candidate does not undergo unacceptable deterioration over its shelf life.

Marketing Application Submission and FDA Review

Assuming successful completion of the required clinical testing, the results of the preclinical studies and clinical trials, along with information relating to the product’s chemistry, manufacturing, controls ("CMC") and proposed labeling, are submitted to the FDA as part of an NDA or BLA requesting approval to market the product for one or more indications. Data may come from company-sponsored clinical trials intended to test the safety and efficacy of a product’s use or from a number of alternative sources, including studies initiated by investigators. To support marketing approval, the data submitted must be sufficient in quality to establish the safety and efficacy of the investigational product to the satisfaction of the FDA. The fee required for the submission of an NDA or BLA under the Prescription Drug User Fee Act ("PDUFA") is substantial (for example, for fiscal year 2024 this application fee is approximately $4.0 million), and the sponsor of an approved NDA or BLA is also subject to an annual program fee, currently more than $415,000 per program. These fees are typically adjusted annually, but exemptions and waivers may be available under certain circumstances. No user fee is required for orphan drug product applications, except when an application also includes an indication for a non-rare disease or condition.

The FDA conducts a preliminary review of all NDAs and BLAs within 60 days of receipt and informs the sponsor by the 74th day after the FDA’s receipt of the submission whether an application is sufficiently complete to permit substantive review. The FDA may request additional information rather than accept an NDA or BLA for filing. In this event, the application must be resubmitted with the additional information. The resubmitted application is also subject to review before the FDA accepts it for filing.

After the submission is accepted for filing, the FDA begins an in-depth substantive review of the application. Under the goals and policies agreed to by the FDA under PDUFA, the FDA has ten months from the filing date in which to complete its initial review of a standard application and respond to the applicant and six months from the filing date for an application with priority review. The review process may be extended by the FDA for three additional months to consider new information or in the case of a clarification provided by the applicant to address an outstanding deficiency identified by the FDA following the original submission. Despite these review goals, it is not uncommon for FDA review of an NDA or BLA to extend beyond the PDUFA goal date.

Before approving an NDA or BLA, the FDA will typically conduct a pre-approval inspection of the manufacturing facilities for the therapeutic/biologic to determine whether the manufacturing processes and facilities comply with cGMPs. The FDA will not approve the product unless it determines that the manufacturing processes and facilities comply with cGMP requirements and are adequate to assure consistent production of the product within required specifications. The FDA also may inspect the sponsor and one or more clinical trial sites to assure compliance with GCP requirements and the integrity of the clinical data submitted to the FDA.

Additionally, the FDA may refer any NDA or BLA, including applications for novel product candidates which present difficult questions of safety or efficacy, to an advisory committee for review, evaluation and recommendation as to whether the application should be approved and under what conditions. Typically, an advisory committee is a panel of independent experts, including clinicians and other scientific experts. The FDA is not bound by the recommendation of an advisory committee, but it considers such recommendations when making final decisions on approval. The FDA also may require submission of a REMS, if it determines that a REMS is necessary to ensure that the benefits of the drug outweigh its risks and to assure the safe use of the drug or biological product. If the FDA concludes a REMS is needed, the sponsor of the NDA or BLA must submit a proposed REMS and the FDA will not approve the NDA or BLA without a REMS.

Under the Pediatric Research Equity Act of 2003 ("PREA"), an NDA or BLA or certain supplements thereto must contain data that are adequate to assess the safety and effectiveness of the product for the claimed indications in all relevant pediatric subpopulations, and to support dosing and administration for each pediatric subpopulation for which the product is safe and effective, unless this requirement is waived, deferred or inapplicable. Sponsors must submit a pediatric study plan to FDA outlining the proposed pediatric study or

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studies they plan to conduct, including study objectives and design, any deferral or waiver requests and other information required by regulation. The FDA must then review the information submitted, consult with the sponsor and agree upon a final plan. The FDA or the applicant may request an amendment to the plan at any time. In general, PREA requirements do not apply to drugs or biologics for indications granted orphan drug designation by the FDA.

The FDA reviews an NDA or BLA to determine, among other things, whether a product is safe and effective for its intended use and whether its manufacturing is cGMP-compliant to assure and preserve the product’s identity, strength, quality and purity. The approval process is lengthy and often difficult, and the FDA may refuse to approve an NDA or BLA if the applicable regulatory criteria are not satisfied or may require additional clinical or other data and information. After evaluating the application and all related information, including the advisory committee recommendations, if any, and inspection reports of manufacturing facilities and clinical trial sites, the FDA may issue either an approval letter or a Complete Response Letter ("CRL"). An approval letter authorizes commercial marketing of the product with specific prescribing information for specific indications. A CRL indicates that the review cycle of the application is complete and the application will not be approved in its present form. A CRL generally outlines the deficiencies in the submission and may require substantial additional testing or information in order for the FDA to reconsider the application. The CRL may require additional clinical or other data, additional pivotal Phase 3 clinical trial(s) and/or other significant and time- consuming requirements related to clinical trials, preclinical studies or manufacturing. If a CRL is issued, the applicant may either resubmit the NDA or BLA addressing all of the deficiencies identified in the letter or withdraw the application. If and when those deficiencies have been addressed to the FDA’s satisfaction in a resubmission of the NDA or BLA, the FDA will issue an approval letter. The FDA has committed to reviewing such resubmissions in response to an issued CRL in either two or six months depending on the type of information included. Even with the submission of this additional information, however, the FDA ultimately may decide that the application does not satisfy the regulatory criteria for approval.

If a product receives regulatory approval from the FDA, the approval is limited to the conditions of use (e.g., patient population, indication) described in the FDA-approved labeling. Further, depending on the specific risk(s) to be addressed, the FDA may require that contraindications, warnings or precautions be included in the product labeling, require that post-approval trials, including Phase 4 clinical trials, be conducted to further assess a product’s safety after approval, require testing and surveillance programs to monitor the product after commercialization or impose other conditions, including distribution and use restrictions or other risk management mechanisms under a REMS which can materially affect the potential market and profitability of the product. The FDA may prevent or limit further marketing of a product based on the results of post-marketing trials or surveillance programs. After approval, some types of changes to the approved product, such as adding new indications, manufacturing changes and additional labeling claims, are subject to further testing requirements and FDA review and approval.

Regulation of Combination Products

Certain products may be comprised of components, such as drug or biologic components and device components that would normally be regulated under different types of regulations, and frequently by different centers at the FDA. These products are known as combination products. We expect to rely on a delivery system, such as pre-filled syringes, pen-injectors and/or autoinjectors to deliver certain of our product candidates. Although we have not yet selected the delivery system to use for administration of such product candidates, including RLYB212 and RLYB116, we expect that, if approved, any such product candidate would be regulated as a combination product, because it is composed of both a drug or biological product and a delivery system “device.”

Under the FDCA and its implementing regulations, the FDA is charged with assigning a center with primary jurisdiction, or a lead center, for review of a combination product. The designation of a lead center generally eliminates the need to receive approvals from more than one FDA center for combination products, although the lead center may consult with other centers within the FDA. The determination of which center will be the lead center is based on the “primary mode of action” of the combination product. Thus, if the primary mode of action of a drug-device combination product is attributable to the drug product, the FDA center responsible for review of the drug product would have primary jurisdiction for the combination product.

A combination product involving a novel drug or biological product and delivery system generally would have a drug or biologic primary mode of action. A combination product with a drug or biologic primary mode of action would be reviewed and approved pursuant to the drug or biologic approval processes. In reviewing the NDA or

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BLA for such a product, however, the FDA review division reviewing the application could consult with their counterparts in the device center to ensure that the device component of the combination product met applicable requirements regarding safety, effectiveness, durability and performance. Approval may require the performance of certain clinical studies, such as clinical usability or human factors studies to demonstrate the safety and/or effectiveness of the device component of the combination product.

Similar considerations apply to regulation of drugs combined with delivery systems outside the United States, including in the EU.

Expedited Programs for Serious Conditions

The FDA is authorized to designate certain products for expedited development or review if they are intended to address an unmet medical need in the treatment of a serious or life-threatening disease or condition. These programs include fast track designation, breakthrough therapy designation, priority review designation and accelerated approval.

To be eligible for a fast track designation, the FDA must determine, based on the request of a sponsor, that a product is intended to treat a serious or life-threatening disease or condition and demonstrates the potential to address an unmet medical need by providing a therapy where none exists or a therapy that may be potentially superior to existing therapy based on efficacy or safety factors. Fast track designation provides opportunities for earlier and more frequent interactions with the FDA review team to expedite development and review of the product. The FDA also may review sections of the NDA or BLA for a fast track product on a rolling basis before the complete application is submitted if the sponsor and the FDA agree on a schedule for the submission of the application sections and the sponsor pays any required user fees upon submission of the first section of the NDA or BLA. Fast track designation may be rescinded by the FDA if the designation is no longer supported by data emerging from the clinical trial process.

In addition, a new drug or biological product may be eligible for Breakthrough Therapy designation if it is intended, alone or in combination with one or more other drugs or biologics, to treat a serious or life-threatening disease or condition, and preliminary clinical evidence indicates that the drug or biologic may demonstrate substantial improvement over existing therapies on one or more clinically significant endpoints, such as substantial treatment effects observed early in clinical development. Breakthrough Therapy designation provides all the features of Fast Track designation in addition to intensive guidance on an efficient development program beginning as early as Phase 1 and FDA organizational commitment to expedited development, including involvement of senior managers and experienced review staff in a cross-disciplinary review, where appropriate. Breakthrough designation may be rescinded by the FDA if the designation is no longer supported.

The FDA may designate a product for priority review if it is a drug or biologic that treats a serious condition and, if approved, would provide a significant improvement in safety or effectiveness. The FDA determines at the time that the marketing application is submitted, on a case-by-case basis, whether the proposed drug or biologic qualifies for priority review. Significant improvement over available therapies may be illustrated, for example, by evidence of increased effectiveness in the treatment of a condition, elimination or substantial reduction of a treatment-limiting drug reaction, documented enhancement of patient compliance that may lead to improvement in serious outcomes, or evidence of safety and effectiveness in a new subpopulation. A priority review designation is intended to direct overall attention and resources to the evaluation of such applications and to shorten the FDA’s goal for taking action on a marketing application from ten months to six months for an original BLA or NDA from the date of filing.

Fast track designation, breakthrough therapy designation and priority review do not change the standards for approval and may not ultimately expedite the development or approval process.

Finally, the FDA may grant accelerated approval to a product for a serious or life-threatening condition that provides meaningful therapeutic advantage to patients over existing treatments based upon a determination that the product has an effect on a surrogate endpoint that is reasonably likely to predict clinical benefit. The FDA may also grant accelerated approval for such a condition when the product has an effect on an intermediate clinical endpoint that can be measured earlier than an effect on irreversible morbidity or mortality ("IMM") and that is reasonably likely to predict an effect on IMM or other clinical benefit, taking into account the severity, rarity, or prevalence of the condition and the availability or lack of alternative treatments. For drugs

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granted accelerated approval, FDA generally requires sponsors to conduct, in a diligent manner, additional post-approval confirmatory studies to verify and describe the product’s clinical benefit. Failure to conduct required post-approval studies with due diligence, failure to confirm a clinical benefit during the post-approval studies, or dissemination of false or misleading promotional materials would allow the FDA to withdraw the product approval on an expedited basis. All promotional materials for product candidates approved under accelerated approval are subject to prior review by the FDA unless FDA informs the applicant otherwise.

Post-approval Requirements

Following approval of a new product, the manufacturer and the approved product are subject to pervasive and continuing regulation by the FDA, governing, among other things, monitoring and recordkeeping activities, reporting of adverse experiences with the product and product problems to the FDA, product sampling and distribution, manufacturing and promotion and advertising. Although physicians may prescribe legally available products for unapproved uses or patient populations (i.e., “off-label uses”), manufacturers may not market or promote such uses. The FDA and other agencies actively enforce the laws and regulations prohibiting the promotion of off-label uses, and a company that is found to have improperly promoted off-label uses may be subject to significant liability.

If there are any modifications to the product, including changes in indications, labeling or manufacturing processes or facilities, the applicant may be required to submit and obtain FDA approval of a new NDA/BLA or an NDA/BLA supplement, which may require the applicant to develop additional data or conduct additional preclinical studies and clinical trials. The FDA may also place other conditions on approvals including the requirement for a REMS to assure the safe use of the product, which may require substantial commitment of resources post-approval to ensure compliance. A REMS could include medication guides, physician communication plans or elements to assure safe use, such as restricted distribution methods, patient registries and other risk minimization tools. Any of these limitations on approval or marketing could restrict the commercial promotion, distribution, prescription or dispensing of products. Product approvals may be withdrawn for non-compliance with regulatory standards or if problems occur following initial marketing.

FDA regulations require that drug and biological products be manufactured in specific approved facilities and in accordance with cGMPs. The cGMP regulations include requirements relating to organization of personnel, buildings and facilities, equipment, control of components and drug product containers and closures, production and process controls, packaging and labeling controls, holding and distribution, laboratory controls, records and reports and returned or salvaged products. The manufacturing facilities for our product candidates must meet cGMP requirements and satisfy the FDA or comparable foreign regulatory authorities’ satisfaction before any product is approved and our commercial products can be manufactured. In addition, for any of our product candidates that include a device delivery system, the device component will be subject to aspects of the Quality System Regulation ("QSR) applicable to medical devices. Manufacturers of drug-device combination products may either opt to comply with all quality regulations governing each component of the product separately, or may take a “streamlined approach” to cGMP that allows the manufacturer to demonstrate compliance with the drug cGMPs along with compliance with several specific provisions from the device QSR—namely, management responsibility, design controls, purchasing controls, corrective and preventive action, installation, and servicing, as applicable.

RLYB US Equity

RLYB · 10-K · period ended 2023-12-31

Item 1. Business.

RLYB US Equity☆

RLYB · 10-K · period ended 2023-12-31

Item 1. Business.

RLYB US Equity